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The Motor Cycle 
Handbook 

The Construction, Operation, Care and 

Repair of Modern Types of Motor 

Cycles, Their Accessories and 

Equipment. 

By 
HAROLD P. MANLY 

Author of "Automobile Upkeep and Care," " The Ford Motor 
Car and Truck," "Automobile Ignition" and "Auto- 
mobile Starting and Lighting." Editor of 
" Brookes' Automobile Handbook." 



ILLUSTRATED 



CHICAGO 

FREDERICK J. DRAKE & CO. 

PUBLISHERS 






Copyright 1920 

By 

FREDERICK J. DRAKE & CO. 



OCT 26 1320 



5CU601153 r 



HUl 



PREFACE 

The Motor Cycle Handbook is a manual cover- 
ing the construction, the operating principles, the 
care and the repair of the newer types of machine. 
Single-cylinder, two-cylinder V-type, two-cylinder 
opposed and four-cylinder engines are treated in 
detail and two-cycle construction has received full 
consideration. Especial attention has been given to 
modern designs in the multi-speed transmission, 
and the various developments in driving clutches and 
their controls. 

The electrical sections w^ill be found complete; cov- 
ering the ignition system in both magneto and battery 
types as well as giving full descriptions of the impor- 
tant dynamo and storage battery lighting equipments. 

In common with the other volumes in this series, 
but little space has been given to historical and theo- 
retical discussion. In almost all cases the principles 
upon which the units operate have been explained by 
reference to parts used in everyday construction by 
well known makers so that the reader will be made 
familiar with the work as actually carried out. 

Methods of repair and adjustment have received 
the greatest consideration in view of the fact that 
these branches of motor cycle work differ materially 
from the corresponding operations as usually per- 
formed in automobile work. The chapter on repairs 
outlines the cautions that should be observed in han- 
dling the engine parts to secure the best results, while 



PREFACE 

units outside of the engine have been considered from 
this standpoint in their respective sections of the 
book. 

Acknowledgment is made of the assistance extended 
to the author by the motor cycle manufacturing trade 
and especial thanks are due i:o the Harley-Davidson 
Motor Company and to the Hendee Manufacturing 
Company for their help in insuring the practical 
value of the material presented. 

The Author. 



TABLE OF CONTENTS 

CHAPTER PAGE 

I The Motor Cycle 9 

Use of Parts — Power Plant — Transmission Sys- 
tem and Driving Parts — The Running Gear 
and Controls. 

II The Motor Cycle Engine 28 

Four-Cycle Principles — Number and Arrange- 
ment of Cylinders — Cooling — Pistons and Pis- 
ton Rings — Connecting Rod and Flywheels — 
Valves and Valve Mechanism — Valve Timing — 
Horsepower — Two-Cycle Engines — Two-Cycle 
Operation and Care. 

III Engine Oiling 83 

Oil Specifications — Requirements of Motor Cy- 
cle Oils — Oiling Methods — Engine Driven 
Pumps — Hand Pumps — Oil Renewal. 

IV The Fuel System 104 

Gasoline — Carburetor Principles — Air Valve 
Carburetors — Plain Tube Carburetors — Manual 
Control Carburetors — Troubles with the Fuel 
System. 

V Magneto Ignition 125 

Ignition Principles — The Breaker — Condenser 
— Magneto — Distributor — Spark Plugs — Mag- 
neto Setting and Care — Berling Magnetos — 
Bosch Magnetos — Dixie Magnetos — Simms 
Magnetos — Magneto and Ignition Trouble. 

VI Dynamo Lighting and Ignition 160 

The Storage Battery— Battery Care— The Dy- 
namo — Current Regulation — Brush and Com- 
mutator Care — Remy Lighting Equipment — 
Splitdorf Lighting Equipment. 



CONTENTS 
CHAPTER PAGE 

VII Driving Parts 192 

Clutch Construction, Adjustment, Care and 
Troubles — Transmission Construction — Sliding 
Gear Types — Planetary Gear-Sets — Kick Start- 
er — Care and Adjustment of Chain Drives — 
Belt and Pulley Care and Adjustment — Brake 
Construction and Adjustment. 

VIII Running Gear 237 

Front Forks — Rear Suspension — Wheels, Rims 
and Hubs — Spoke Care — Tire Construction — 
Care, Abuse and Repair of Tires. 

XI Power Attachments and Side Cars 261 

Briggs & Stratton Motor Wheel — Johnson Mo- 
tor Wheel — The Cyclemotor — Side Cars — Side 
Car Attachment and Care. 

X Motor Cycle Repairs 278 

Tools Required — Cylinder Removal and Re- 
placement — Cylinder Walls — Carbon Removal 
and Prevention — Piston Removal and Replace- 
ment — Fitting New Pistons — Fitting Piston 
Pins — Squaring Pistons — Rounding Piston 
Skirt — Aligning Connecting Rods— Fitting Pis- 
ton Rings — Roller Bearings — Fitting Fly- 
wheels — Aligning Crankshafts — Crankcase 
Bearings — Valve Troubles — C ompression 
Losses — Valve Grinding — Refacing and Ream- 
ing Valves — Valve Clearance Adjustment — 
Valve Springs. 

Index 314 



THE MOTOR CYCLE HANDBOOK 



CHAPTEE I 
THE MOTOR CYCLE 

The modern motor cycle is distinguished from its 
predecessors chiefly by the adoption of many features 
similar to standard automobile construction and 
design. While the early two- wheeler consisted of lit- 
tle more than an engine driving an ordinary bicycle, 
the latest developments retain little of the bicycle 
except the use of only two wheels. Otherwise motor 
cycles are miniature automobiles. 

Motor cycles in general are among the finest exam- 
ples of mechanical genius and skill in workmanship. 
The average motor cycle is a finer mechanism than 
the average automobile; the truth of this statement 
being proven by the fact that a machine weighing 
only about four hundred pounds will easily negotiate 
good, bad and indifferent roads at speeds that would 
wreck a car regardless of the car's greater size and 
apparent strength. 

Few outside of the motor cycle industry realize the 
extreme accuracy that is used in the manufacture of 
these machines. The fitting of parts is gauged to 
within thousandths of an inch and in many cases to 
fractions of the thousandth. Adjustments are pro- 

9 



10 THE MOTOR CYCLE HANDBOOK 

vided for practically every point of wear and the 
materials of the wearing parts are the best that mod- 
ern engineering can produce. 

Motor cycle repairing calls for better work than 
is required in handling almost any other type of auto- 
motive apparatus and it is essential that those han- 
dling this class of work thoroughly understand the 
functions and operating conditions of the parts which 
they handle. 

PARTS OF THE MOTOR CYCLE 

The motor cycle may conveniently be divided into 
three principal groups of parts; the power plant, the 
transmission system, and the running gear. 

The power plant includes the engine with its cylin- 
ders, crankcase, pistons, connecting rods, crankshaft 
and so on. The engine auxiliaries which complete the 
power plant include the fuel system for furnishing a 
combustible gas, the ignition system for firing the gas, 
a lubrication system for preventing wear, and a cool- 
ing system for maintaining the parts at safe operating 
temperatures. 

The transmission system begins at the engine, where 
it receives power. This power goes through the clutch 
and the gear-set, usually called the transmission, and 
thence to the driving wheel through chains or belts 
or shafts. The clutch, gear-set and drive thus make 
up the complete transmission. 

The running gear includes the road wheels and 
their tires, the frame and front forks with their sus- 
pension or method of attachment to the wheels, also 
the suspension for the rider's seat and for the handle 
bars. 



THE MOTOR CYCLE 



11 




12 THE MOTOR CYCLE HANDBOOK 

Various control members are required in each of 
the three divisions. The power plant requires con- 
trols for the fuel or carburetor, for the ignition or 
spark, and sometimes for the oiling system as well. 
The transmission system includes controls for the 
clutch and for the various gear ratios provided in the 
gear-set. The running gear includes controls for the 
brakes, while the handle bars as steering controls 
might also be considered as members of this general 
class. 

THE POWER PLANT 

The Engine. — Two distinct types of engine are in 
use. One of these types, called the four-cycle engine, 
is in the majority. The four-cycle engine delivers 
one power impulse in each cylinder for every four 
strokes of the piston or two complete revolutions of 
the crankshaft. The other type is called a two-cycle 
engine and this one delivers one power impulse for 
each two strokes of the piston or for each revolution 
of the crankshaft. 

Motor cycle engines differ in the number of their 
cylinders, most of them at present being of the two 
cylinder variety, while four cylinders show a gain in 
number of users. Single-cylinder models retain their 
popularity, especially in medium and light-weight 
machines. Most of the single-cylinder engines have 
their cylinders set vertically and all of the four-cylin- 
der machines use such a mounting. Two cylinders are 
generally set in a "V" arrangement at an angle to 
each other, although in some cases these engines are 
of the horizontal opposed type with the two cylinders 
lying flat and in line with each other. 

Most single and twin-cylinder engines are equipped 



THE MOTOR CYCLE 



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14 THE MOTOR CYCLE HANDBOOK 

with two flywheels, both carried inside the erankcase, 
but either of these types may also have an outside 
wheel. Four-cylinder engines generally have their 
single flywheel enclosed in a housing at one end of 
the row of cylinders, this being part of the unit 
power plant as often found in automobile construc- 
tion. 

Cooling. — American motor cycles are of the air- 
cooled type in which the cylinder castings are pro- 
vided with a number of flanges or ribs which furnish a 
great amount of surface exposed to the circulation of 
outside air while the machine is in motion. While 
water cooling has been successfully employed in a 
number of foreign models, it has not yet gained any 
foothold in the United States. 

Fuel System. — The chief part of this portion of the 
power plant is the carburetor, a device which changes 
the liquid fuel to a vapor and mixes this vapor with 
the necessary amount of air to form a combustible 
gas in the engine cylinders. Recent improvement and 
development of the carburetor has been rapid, this 
having been necessary in order to care for the con- 
stantly decreasing quality of the fuel available. 

Aside from the carburetor the fuel system includes 
the supply tank with the required valves and pipe 
lines for making the connections between the units. 

Lubrication System. — The motor cycle engine, being 
air-cooled, operates at a high temperature when com- 
pared with automobile engines, which are generally 
water-cooled. The air circulation depends on the 
rapidity with which the motor cycle is moving through 
the air, so that when pulling hard at low speed there 
is a decided rise in heat. 

These peculiar conditions of operation make it nee- 



THE MOTOR CYCLE 



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16 THE MOTOR CYCLE HANDBOOK 

essary that the engine lubrication or oiling system be 
so designed and constructed that it unfailingly sup- 
plies the requisite amount of oil to all of the moving 
parts under all conditions of operation. 

Single and twin-cylinder engines are usually fitted 
with an oiling system whose supply tank is adja- 
cent to, or a part of, the fuel tank. Four-cylinder 
types may carry the oil supply in the bottom of the 
engine crankcase or they also may be provided with 
a separate tank. 

From the tank or oil reservoir the lubricant is 
delivered through a pump to the crankcase and in 
some cases directly to other parts of the engine mech- 
anism. Many types of pumps are in use, some being 
positively driven from the engine, while others are 
operated by hand as the occasion may require. Engine 
driven pumps are generally of the plunger type, but 
are sometimes of the gear type in which the gear teeth 
force the oil through the pump. Hand pumps are 
of the plunger type in all cases. 

Ignition System. — Electric current for producing 
an ignition spark may be furnished either by a dynamo 
which is used also for lighting purposes or by a mag- 
neto used for ignition only. Both types are in com- 
mon use, the magneto still being in the majority, 
although the dynamo and battery system is becoming 
popular due to the desirability of the electric lighting 
which accompanies it. 

The dynamo system includes the generating unit and 
current regulating devices, also the storage battery, 
all of which are common to both the ignition and the 
lighting system. The ignition parts include a coil 
for increasing the current's voltage, a breaker for 
causing the spark to pass at the desired time and a 



THE MOTOR CYCLE 



17 



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18 THE MOTOR CYCLE HANDBOOK 

distributor for sending the current to the proper cyl- 
inder. In each cylinder is a spark plug between 
whose points or electrodes the spark passes and the 
ignition system is completed by the necessary wiring 
and switches. 

The magneto system is more nearly self contained 
than is the battery system, inasmuch as the magneto 
not only generates the current but also includes within 
itself the breaker and distributor. Motor cycle mag- 
netos of the true high tension variety generate the 
current at low voltage and then change it to a high 
tension or high voltage current without additional 
parts. 

THE TRANSMISSION SYSTEM 

Clutch. — The clutch enables the rider to connect 
the engine with the balance of the transmission system 
or to disconnect it at will. That is, the clutch pro- 
vides a means whereby the power of the engine may 
be used to drive the motor cycle or by means of which 
the cycle may remain at a standstill while the engine 
still runs. 

The almost universally used type of motor cycle 
clutch consists of a number of flat rings or disks 
laid flat against one another. Every other disk is con- 
nected with the engine so that it is driven when the 
engine runs, while the intervening disks are connected 
with the transmission or the drive to the wheel. 

The disks are normally held pressed together by 
springs so that they all revolve as a unit. Under this 
condition the engine's power is sent to the driving 
parts and the clutch is said to be engaged. With the 
spring pressure released the disks separate and each 
set may revolve independently of the other set, thus 



THE MOTOR CYCLE 



19 




20 THE MOTOR CYCLE HANDBOOK 

allowing the engine to run free witti the clutch dis- 
engaged or released. 

Some of these clutcnes operate m a bath of oil, 
while others allow the disks to remain dry. The 
clutch is carried either with the gear-set or is mounted 
on the engine housing. It is operated by the rider 
with a foot pedal, or a hand lever or grip, and in some 
machines by both of these control members. 

The Gear-Set. — The power developed by an inter- 
nal combustion engine such as used in motor cycles 
is in almost direct proportion to the speed at which 
the engine is running; that is, the greater the speed 
the greater will be the power. It will be recognized 
that under some conditions of slow running a great 
amount of power may be called for, this being true 
when driving through deep sand or mud. It is there- 
fore desirable to provide means for operating the 
engine at various rates of speed while the cycle's 
speed remains constant, and this is accomplished by 
the gear-set. 

The greatest number of motor cycles provide three 
different ratios or reductions of speed between the 
engine and the driving wheel. Some, however, have 
but a single ratio or a direct drive; others have two 
different ratios; while still others are fitted with three 
ratios for forward motion with a fourth one for driv- 
ing backward or a reverse. 

In the three speed machine high gear provides the 
least reduction of engine speed and is therefore used 
for ordinary driving with the motor cycle running at 
medium and high speeds on the road. Intermediate 
or second speed provides a greater reduction so that 
the engine can run fast enough to enable the cycle 
to climb steep hills or to pass over bad road condi- 



THE MOTOR CYCLE 



21 




22 THE MOTOR CYCLE HANDBOOK 

tions. Low speed or first speed allows the engine to 
run ten or twelve times as fast as the road wheel turns 
and this ratio is used in starting from rest and for 
driving through extremely bad going. 

The usual gear-set consists of two series of gears 
mounted on parallel shafts. The gears carry varying 
numbers of teeth so that with different pairs brought 
into engagement with each other, different ratios of 
speed are obtained between the two shafts. One shaft 
is connected with the engine while the other is con- 
nected with the drive to the road wheel. The speed 
changes are generally controlled by a hand lever which 
may be easily moved by the rider. 

The Starter. — Whereas the old-time motor cycle 
was started by pedaling it along the road or else by 
running along side until the engine was started, almost 
all of the newer models are provided with what is 
called a "kick starter." 

The starter consists of a foot pedal carried at the 
outer end of an arm, the arm being connected 
with a toothed segment or with a small gear. This 
segment or gear engages with another gear connected 
to the transmission in such a way that pressure of the 
operator's foot on the pedal causes the engine crank- 
shaft to go through one or more revolutions. With 
the controls properly manipulated, this cranking starts 
the engine. 

Drive. — From the preceding description it will be 
seen that the power generated in the engine must be 
carried to the gear-set and from the gear-set it must 
be carried to the driving wheel. The drive itself may 
thus be considered as of two parts in the standard type 
of machine ; first from the engine to the gear-set, and 
second from the gear-set to the rear wheel. 



THE MOTOR CYCLE 



23 




24 THE MOTOR CYCLE HANDBOOK 

Chains are the means usually employed for both 
parts of the drive. "With the engine and gear-set con- 
structed as separate "units and mounted independently 
of each other, chain drive is almost universal prac- 
tice between these two parts. "With the engine and gear- 
set built as a unit power plant and held in permanent 
alignment and relation with each other the drive be- 
tween them is by means of a direct extension of the 
crankshaft or through bevel or worm gears. 

In machines driving directly from the engine to the 
road wheel, this class including most of those having 
but a single speed ratio, the drive is usually taken 
through a belt either of flat or V type. Drive from 
the gear-set to the rear wheel is usually carried 
through a chain, although a belt may sometimes be 
used at this point. 

THE RUNNING GEAR 

Motor cycle frames are constructed of steel tubing 
and pressed steel. In general outline they bear a dis- 
tinct resemblance to the ordinary diamond type of 
bicycle frame. They are, however, larger and stronger 
and are so shaped as to accommodate the engine, the 
gear-set, the supply tanks, and the generally heavier 
wheels and hubs of the motor cycle. 

The front or steering wheel is carried between forks 
mounted in a head provided with bearings. Control 
of direction is through the handle bars. In a few ma- 
chines the front forks are of trussed construction, but 
in the great majority of designs the forks include 
springs and are built in two parts connected by rocker 
levers or arms. One part is attached directly to the 
wheel hub while the other part is carried by the frame 



THE MOTOR CYCLE 



25 



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26 THE MOTOR CYCLE HANDBOOK 

head. Relative movement between the parts is con- 
trolled by springs of either coiled or leaf type. 

While the rear wheel is often carried between rigid 
extensions of the frame, it may also be spring mounted 
in some designs, leaf springs being most often used at 
this point. The rider's saddle is usually built with 
coiled springs and the saddle may be carried either 
by a seat post extending down into one of the frame 
members or it may be mounted on a bar which is 
pivoted at one end. Either the bar or the seat post 
may then be fitted with springs so that easy riding 
qualities are secured. 

At the present time all standard motor cycle wheels 
are of the wire spoke type although disk wheels and 
wood spoke wheels have their advocates and are used 
to some extent. The distance between the hub of the 
front wheel and the hub of the rear wheel is meas- 
used as the wheelbase of the motor cycle. This dis- 
tance varies between fifty and sixty-five inches, about 
fifty-seven inches being the average wheelbase in use. 

Tire sizes are growing larger year by year. Vfhile 
some tire sections as small as two inches are still found, 
the greater number of machines carry three-inch in 
both front and rear and many are using three and one- 
half-inch tires. The outside diameter or height of the 
tire is usualty twenty-six, twenty-seven or twenty-eight 
inches. 

Brakes, — In American practice the brakes are placed 
on the rear wheel only, although many foreign ma- 
chines have front wheel brakes in addition to those 
used on the rear. Again, the American practice at- 
taches the brakes so that they operate directly on the 
rear hub or at least on drums attached to the rear 
hub. In many foreign designs the rear wheel brakes 






THE MOTOR CYCLE 



27 



act on the pulley carrying the driving belt and which 
is attached to the rear wheel rim or to the spokes. 

The most generally used type of brake is that formed 
by a band contracting on a drum. Some machines use 
a brake constructed of internal shoes which expand 
within a drum while others use both the contracting 
and expanding brakes operating on the one drum. 
Many of the light weight machines use coaster types 
of brakes similar in design to those employed on bi- 
cycles but heavier in construction. 

The brake is generally operated by a foot pedal on 
the right hand side of the machine the same as in 
automobile practice. Some cycles use a left hand pedal 
for the brake while others control from a hand lever 
attached to one of the handle bars near the grip. 



The 
Motor 
Cycle 





Engine 




Cooling 


Power Plant 


Fuel 




Lubrication 




Ignition 




^Clutch 


Transmission System 4 


Gear-Set 
Starter 




Drive 




Frame 




Front Forks 


Running Gear 


Suspension 




Wheels and Tires 




Brakes 



s 



CHAPTER II 
THE MOTOR CYCLE ENGINE 

Of the two types of engine the four-cycle is much 
more commonly used than is the two-cycle and it will 
be the four-cycle type that will be treated in detail 
through the first portion of this chapter. The two- 
cycle engine differs materially from the four-cycle 
type, not only in its principle of operation but also 
in its construction and in many of the accessories 
used to complete the power plant. 

The elementary parts of the four-cycle engine as 
shown in Figure 9 include the following: First, the 
cylinder which is closed at one end and open at 
the other. Within the cylinder is a piston which 
is likewise closed at one end and open at the other. 
The closed end of the piston is toward the closed 
end of the cylinder. The piston is adapted to slide 
back and forth within the cylinder and with the 
force of the burning fuel acting between the closed 
cylinder head and the top of the piston, this latter 
member is forcibly driven toward the open end of 
the cylinder. 

In order to prevent the piston from being driven 
all the way out of the open end of the cylinder and 
also in order that the reciprocating motion of the 
piston may be turned into a rotary motion suitable for 
driving the cycle, the piston is attached to one end of 

28 



THE MOTOR CYCLE ENGINE 



29 



a connecting rod while the other end of this rod is 
attached to a crank pin. The crank pin is in turn 
supported by the crankshaft or by the flywheels and 
the bearings mounted in the crankcase. 




Figure 9. — Single-Cylinder Engine Cut Open to Show the 
Cylinder, Piston, and Connecting - Rod Construction. 



The length of the connecting rod is such that the 
piston can at no time travel all the way to the 



30 THE MOTOR CYCLE HANDBOOK 

closed end of the cylinder. At the extreme limit 
of piston travel there is still a certain space remain- 
ing between the top of the piston and the head of 
the cylinder. This is called the combustion space 
and within it is carried the inflammable mixture 
which is burned to produce power. It will be evi- 
dent that means must be provided for allowing fresh 
gas to enter the combustion chamber and means must 
also be provided for allowing the spent gas to escape 
from this chamber. The passage of gas takes place 
through two valves, one of which called the inlet 
valve admits fresh gas while the other one, called 
the exhaust valve, allows escape of the burned gas. 

THE FOUR-STROKE CYCLE 

With the engine ready to start, the piston is at 
the top of its stroke by which is meant that the pis- 
ton is as near to the cylinder head as it can come. 
The crankshaft is caused to revolve, and through the 
connecting rod this turning of the crankshaft draws 
the piston away from the cylinder head. At the 
same time, the inlet valve is caused to open and 
fresh gas is drawn into the cylinder through a pipe 
connected with the carburetor. Immediately follow- 
ing the end of the inlet stroke, when the piston has 
traveled as far away from the cylinder head as it 
can go, the inlet valve closes. This travel of the 
piston away from the cylinder head is called the 
inlet stroke. This and the remaining strokes of the 
cycle are shown in Figure 10. 

During the inlet stroke the exhaust valve has been 
closed and now that the inlet valve has also closed, 



THE MOTOR CYCLE ENGINE 



31 




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Figure 10. — Position of the Valves During- the Pour Stroke© 

of the Four-Cycle Engine. Upper Left: Inlet. 

Upper Right: Compression. Lower Left: 

Power. Lower Right : Exhaust. 



32 THE MOTOR CYCLE HANDBOOK 

the fresh gas is driven ahead of the piston and up 
into the combustion space by continued rotation of 
the crank. It is necessary to thus compress the gas 
so that it will easily ignite and so that it will develop 
the required power upon burning. This second stroke 
during which the piston travels back toward the cyl- 
inder head is called the compression stroke. 

At the end of the compression stroke, an electric 
spark is caused to pass through the highly compressed 
gas and the mixture is ignited. The heat developed 
in the burning mixture causes a great expansion in 
volume and the pressure that is generated drives the 
piston back toward the open end of the cylinder. 
This third stroke is called the power stroke and its 
force is utilized to turn the engine's crank pin and 
the flywheels so that power is delivered to the trans- 
mission system and driving parts. 

At the end of the power stroke, the cylinder is 
filled with spent gas and in order to get rid of this 
gas, the exhaust valve is opened. Further rotation 
of the crankshaft drives the piston back toward the 
head of the cylinder, forcing the old gas out through 
the exhaust valve. This is called the exhaust stroke. 

These four strokes; inlet, compression, power and 
exhaust; complete the cycle and leave the piston at 
the head of the cylinder ready to start over again. 
The exhaust valve is closed and the inlet valve is 
again ready to open. This same sequence of events 
takes place in each cylinder of every four-cycle engine. 
It is the fundamental principle of engine operation 
and should be thoroughly fixed in the mind, both as to 
the functions and actions during each stroke and as to 
the order in which the strokes occur one after another. 



THE MOTOR CYCLE ENGINE 
NUMBER AND ARRANGEMENT OF CYLINDERS 



33 



Motor cycle engines are made with either one, two 
or four cylinders. The single-cylinder engine admits 




Figure 11. — Valve Operating- Parts of V-type Engine 
(Reading- Standard), 

of but slight variation in the cylinder's position 
although even in this case it may be mounted either 
verticallv or inclined. 



34 THE MOTOR CYCLE HANDBOOK 

Two-Cylinder Engines. — This type which is in the 
majority will be found in two distinctly different 
arrangements. According to the generally adopted 
method, the cylinders are set at an angle to each 
other forming what is known as a V engine as shown 
in Figure 11. The greatest angle allowed between 
the cylinders is ninety degrees but this great opening 
is seldom found. Most V engines are built with an 
angle of either forty-five degrees or forty-two degrees 
between the axes of their cylinders. 

The other type of two-cylinder engine is known 
as the horizontal opposed. In this type the cylinder 
axes extend in opposite directions as shown in Figure 
12. As far as motor cycles are concerned, this 
opposed twin is a comparatively recent development, 
although this was one of the earliest methods of con- 
struction used in automobile practice. Each type of 
engine has certain advantages and also certain dis- 
advantages. 

The V engine is especially adapted to motor cycle 
construction because it fits easily into the frame that 
is generally adopted. This engine is compact and 
allows the use of short passages for the gas between 
the carburetor and the combustion spaces. The nearly 
upright position of the cylinders allows very good 
cooling. One of the disadvantages of the V engine 
is found in the unequal intervals between the firing 
strokes of the front cylinder and the rear one, and 
of the firing strokes between the rear cylinder and the 
front one. As an example, the interval measured in 
degrees of the circle when applied to a V engine of 
forty-two degrees, will be found to amount to 402 
degrees between the ignition points of the front cylin- 
der and the real cylinder while it only amounts to 



THE MOTOR CYCLE ENGINE 



35 




36 THE MOTOR CYCLE HANDBOOK 

318 degrees between tne rear cyimaer and the front 
cylinder. At extremely low speeds this might cause 
some unevenness of operation, but because the motor 
cycle engine is of the high speed type, this apparent 
unevenness is not noticeable. Some difficulties are 
encountered in the matter of mechanical balance be- 
cause of the fact that both pistons are within a few 
degrees of each other, moving upward at the same 
time and moving downward at the same time. 

The opposed cylinder engine has the mechanical 
advantage of excellent balance because both pistons 
start away from the cylinder heads at the same 
instant and they both arrive at the other end of 
their strokes at the same instant. Furthermore, their 
velocity is the same at all times during the stroke. 
Thus, the reciprocating parts balance each other in 
the two cylinders. Unless the two-cylinder opposed 
engine is mounted crosswise of the motor cycle frame 
some difficulty may be found in cooling. That is, the 
rear cylinder will not always cool as readily as will 
the front one. The opposed twin makes the design of 
the inlet passages more difficult because of the com- 
paratively great distance between the combustion 
spaces of the two cylinders. 

Four-Cylinder Engines. — One of the more recent 
developments in motor cycle design has been the adop- 
tion of the four-cylinder vertical engine by a number 
of makers. A section through one such engine is 
found in Figure 13, and it will be seen that the design 
is almost identical with automobile practice except 
that the cooling is by air instead of by water. The 
cylinders are carried one behind the other mounted 
on a crankcase which supports the lengthwise crank- 
shaft. In the particular example shown, the clutch 



THE MOTOR CYCLE ENGINE 



37 




SS THE MOTOR CYCLE HANDBOOK 

and transmission form a unit with the engine, 
although this is not a necessary characteristic of four- 
cylinder engines any more than of other types. 

Cylinder Design. — The cylinders of motor cycle 
engines are made from cast iron having a fine smooth 
grain. This material is adopted because of its com- 
parative freedom from warping under heat and also 
because it readily takes on a high polish and very 
smooth surface for the interior of the cylinder walls. 

The cylinders are formed with a flange at their 
lower or open end. This flange is bolted to the crank- 
case. In the majority of designs, the cylinder is made 
of one single casting but in some designs the top or 
head of the cylinder, that portion forming the com- 
bustion space, is made separately from the lower part. 
Detachable cylinder heads are adopted to facilitate 
the manufacturing processes of boring and grinding 
and as a general rule the detachable head is supposed 
to remain in place at practically all times during the 
life of the engine. This is contrary to automobile 
practice in which a separate cylinder head is designed 
to be removed for such purposes as carbon removal 
and valve grinding, 

COOLING 

The problem of keeping the temperature of the 
cylinder walls and of the piston at a point sufficiently 
low to allow for lubrication is one of the greatest 
importance in any internal combustion engine but 
it is of especial importance in the motor cycle engine 
because of the high speed at which these units are 
operated. 

The maximum heat of the burning gas rises to a 



THE MOTOR CYCLE ENGINE 



point almost as high as the melting point of iron so 
that it is plain this heat must be almost instantly dis- 
sipated. Of course, the greater part of the heat dis- 
appears through the expansion of the gases, but there 
is still a very considerable remainder to be taken 




Figure 14.- 



-Air Cooling- Flanges on Single-Cylinder Engine 
(Cyclemotor). 



away from the metal parts of the engine. It is almost 
a universal practice in motor cycle design to use air 
cooling by which the excess heat is directly carried 
away from the cylinder walls by air currents. This 
is known as direct cooling as opposed to indirect radia- 
tion through the water cooling system generally used 
upon the automobile. 



40 



THE MOTOR CYCLE HANDBOOK 




Figure 15. — Air-Cooled Engine Fitted With Fan (Spacke). 



THE MOTOR CYCLE ENGINE 



41 




Fignre 16.— Cooling Flanges on a Four-Cylinder Engine 
(Henderson). 



42 THE MOTOR CYCLE HANDBOOK 

Motor cycle cylinders are made with a large num- 
ber of thin fins or flanges generally arranged as shown 
in Figure 14. The heat of combustion is absorbed 
by the cylinder walls and transmitted to the cooling 
flanges. The air that passes through and around these 
flanges whenever the machine is in motion, serves to 
rapidly reduce their temperature so that the maxi- 
mum at any exposed point of the engine is held 
between three hundred and four hundred degrees. 
The water-cooled engine has its cylinder walls kept 
between one hundred and fifty and two hundred 
degrees under ordinary conditions. 




Figure 17. — Exhaust Muffler Fitted With Cut-Out (Reading 
Standard). 

While, in a few cases, a fan has been fitted as 
shown in Figure 15, this practice is not often fol- 
lowed, the draft of air induced by motion of the 
motor cycle being depended upon for circulation. The 
cooling arrangement of a four-cylinder engine is shown 
in Figure 16. 

Because the cooling depends on circulation of air 
and because this circulation depends on movement of 
the motor cycle, it is dangerous to run the engine 
for any length of time with the cycle idle. Such a 
practice will cause overheating and will easily result 
in scored cylinder walls. 



THE MOTOR CYCLE ENGINE 43 

PISTONS AND PISTON RINGS 

The pistons of all internal combustion engines are 
of the same general design. They are closed at the 
upper or cylinder-head end and open at the lower 
or crankcase end. There are a great many variations 
in the details of design, many of which may be noted 
from the sectional drawings of engines in this and 
other chapters. The piston is made a few thousandths 
of an inch smaller in its outside diameter than the 
inside diameter of the cylinder, this being necessary 
to allow the piston to make a running fit. Even 





Figure 18.— Piston Rings. Left: Step Joint. Right: 
Diagonal Joint. 

though a piston might be fitted closely enough to 
make a gas-tight joint when first manufactured, this 
gas tightness would disappear as soon as some wear 
took place and it is therefore necessary to provide 
special means for retaining a tight seal between the 
outside of the piston and the inside of the cylinder. 
This seal is secured by the piston rings. 

The piston rings are made from cast iron and are 
carried in grooves cut around the outside surface of 
the piston and in most cases near the top. The rings 
are cut through at one side as shown in Figure 18. 
This cutting allows them to be slipped into place over 
the outside of the piston and to then drop into their 
slots. It will be noted from several of the illustra- 



44 THE MOTOR CYCLE HANDBOOK 

tions that some makers use two rings while others 
use three and that some makers place all of the rings 
near the top of the piston while others place one of 
them near the lower end of the piston and the remain- 
der near the top. A section through a typical motor 
cycle engine is shown in Figure 19 and from this 
drawing the general construction of the piston and 
the location of its rings may be seen. 

In addition to the piston rings many designs cut 
a comparatively shallow groove at one or more points 
around the piston, these being known as oil grooves. 
The purpose of this groove is to collect the excess oil 
from the cylinder walls and to allow this excess to pass 
through small holes drilled into the bottom of the 
groove and thence through to the crank chamber. 
Some pistons are also drilled with rather large holes at 
various points around their circumference. These 
holes not only serve to lighten the weight of the 
piston but also allow a better distribution of the 
oil spray over the cylinder walls. Pistons having three 
piston rings, one oil groove and drilled holes, are 
shown in Figure 20. 

CONNECTING ROD AND FLYWHEELS 

The connecting rod, which serves as a driving unit 
between the piston and crankshaft or crank pins, is 
generally of an I section made thus for a combina- 
tion of lightness and strength. In many designs the 
upper end of the connecting rod carries a bushing and 
this bushing encloses a hardened steel rod or tube 
which is called the piston pin. The piston pin is 
mounted in bosses formed in the walls of the piston. 
In other designs the bushings are mounted in the pis- 



THE MOTOR CYCLE ENGINE 



45 




Figure 19. — Constructional Details of Engine Having* Ball 
and Roller Bearings in the Crankcase (Spacke). 



46 



THE MOTOR CYCLE HANDBOOK 




Figure 20. — Piston Construction Showing- Three Rings and 

One Oil Groove Below. The Connecting Rods 

Are Mounted on Two Separate Crank 

Pins (Iver-Johnson). 



■TOR CYCJLE • 



47 



and the piston pin ii elamped in the connecting 
rod. The Idwer end of the r :orj rj <-:r-t i rjrr pod earri 

ich j rj motor cycle practice may be ol the 
.■<. the roller or the ball type, Thii i i generally 

called t.fio hjf/ ond h^rin^. 

Thr; Mr> <:rj r J \)('/,irir\» f;iv:lo.s<;s t.h'r '-.rank pin and t.fv; 

Kh pin, iu Q3 cU pra oerally 










nod between tin ipported by die 

wheels, In may term a 

of the lid then 

bed to H laft bnt the ftnrt mentioned 

the r >n f - generally cued tti application 

. in man;/ <rf the ill 

ter. An example of the connecting v<><\ attached 



48 THE MOTOR CYCLE HANDBOOK 

crank pin formed integral with the crankshaft is shown 
in Figure 21. This illustration also shows counter- 
weights attached to the crankshaft, these counter- 
weights serving to balance in some degree the motion 
of the reciprocating piston. 

In single-cylinder and in twin-cylinder V type 
engines two flywheels are commonly employed, both 
being mounted inside of the crankcase. In some small 
single-cylinder engines, but one flywheel is used and 
this wheel may be carried either inside or outside of 
the crankcase. In opposed twins and in four-cylinder 
vertical engines, only a single flywheel is used and 
this is usually mounted outside of the crankcase at 
one end of the engine. The flywheels may be made 
from drop forgings or from cast iron. When the 
crank pin is attached directly to the flywheels, a part 
of the wheel is made heavy at a point opposite the 
crank pin, this heavy portion acting as a counter- 
weight. 

It will be found that in a majority of engine designs 
using the twin-cylinder V principle of construction, 
the lower or crank pin ends of both connecting rods 
are mounted on one and the same pin so that their 
angular position with reference to the flywheel rim 
is the same for both rods. It has been already 
explained that the interval between power strokes in 
the V engine is unequal between the two cylinders 
but in one form of construction this uneven interval 
is not present. This is the form of construction that 
is shown in Figure 20 and in Figure -22. 

Eeference to Figure 22 will make clear the effect 
secured with each of the two constructions. The 
upper drawing shows the general practice with both 
connecting rods attached to a single crank pin. It 



THE MOTOR CYCLE ENGINE 



49 





Figure 22. — Variations in Piston Position Due to the Use 
of One or Two Crank Pins. 



50 THE MOTOR CYCLE HANDBOOK 

will be seen that while one piston is at top dead 
center, the other one has either started on its down 
stroke or else has not finished its upward stroke. This 
difference of piston position accounts for the variation 
in the time interval between firing strokes. In the 
lower drawing is shown the construction which mounts 
each connecting rod on its own individual crank pin 
and it will be seen that both pistons are at their upper 
dead centers at the same time. This latter construc- 
tion allows an even firing interval between the two 
cylinders. 

Believing Crankcase Pressure. — The reader 
undoubtedly will have noticed that the bulk of the 
flywheels, when these are enclosed within the crank- 
case, almost completely fills the space in the case. 
It will be realized that when the piston is on its 
down stroke, the air in the crankcase must be rapidly 
compressed because the piston displacement is large 
when compared with the unfilled space in the crank- 
case. It will also be evident that the upward stroke 
of the piston will produce a considerable vacuum in 
the crankcase. The alternating pressure and vacuum 
that would thus be present would tend to force oil 
above the piston and also to force the oil out through 
the crankshaft or flywheel bearings. To overcome this 
leakage of oil, some method is usually provided by 
which the pressure is relieved or by which both pres- 
sure and vacuum are relieved. 

The relief valve is mechanically operated in most 
designs and is attached to some part of the gearing 
which operates the inlet and exhaust valves because, 
of course, the relief valve must keep time with the 
movement of the piston. In one design there is a 
rotary valve consisting of a slot cut into the shaft 



THE MOTOR CYCLE ENGINE 



51 



carrying one of the gears and this slot registers with 
the opening when the piston has just started down 
on the firing stroke. The registering of these two 
openings gives the air a point of escape. 




Figure 23. — Poppett Valve Action. The Left-Hand Valve 

Is Open and the Rig-ht-Hand One 

Closed (Iver- Johnson). 



VALVES 



The openings in the combustion chamber of the 
engine through which the gases pass when coming into 
and leaving the cylinder are closed by a poppet form 
of valve. This is the type of valve often defined as 
a lift valve. Its construction is shown in Figure 23. 
The various parts of the valve are defined as follows: 



52 THE MOTOR CYCLE HANDBOOK 

The head is the flat circular piece that closes the open- 
ing in the combustion chamber. The head is attached 
to a long rod called the valve stem. The valve stem 
passes through a support called the valve-stem guide. 
The part of the opening into the combustion space 
against which the edge of the head rests with the 
valve in place is called the valve seat, and the part 
of the head which rests against the seat is called the 
valve face. 

The face and seat of the valve are formed at an 
angle with the main body of the head and with the 
valve stem. This angle is sometimes thirty degrees 
with the head, such construction being oftentimes used 
for the inlet valves. An angle of forty-five degrees 
is more commonly used and is generally found in the 
exhaust valves, even though thirty degrees may be 
used for the inlets in the same engine. 

The valve is held on its seat by means of a coiled 
spring. The lower end of the valve spring is attached 
to the lower end of the valve stem by various methods 
using keys, pins and slotted washers. The upper end 
of the valve spring rests against or is indirectly sup- 
ported from the metal of the cylinder. In Figure 23, 
one valve is shown open, that is, raised from its seat 
with its spring compressed. The other valve is shown 
closed, resting on its seat with its spring extended. 

VALVE-LIFTER MECHANISM 

The valves are closed by their springs and when it 
is desired to open them, the spring pressure is over- 
come by the action of a cam which lifts the lower end 
of the valve stem through a device called the valve- 
lifter. The valve-lifter may take any one of a great 



THE MOTOR CYCLE ENGINE 



53 






o 

1 

o 



3 

(-t-Oi 






w 
o 

5' 

o 

o 

3 




54 



THE MOTOR CYCLE HANDBOOK 



variety of forms depending upon the ideas of the 
designer. A cam, as used in motor cycle work, may 
be defined as a roller having a projection at some 




Figure 25. — Cams and Valve Lifters in V-Type Engine 

(Emblem). 

point around its circumference or having several pro- 
jections at various points. 

One of the simplest forms of valve operating mech- 






THE MOTOR CYCLE ENGINE 55 

anism is shown in Figure 24. The valve for the left- 
hand cylinder is shown in its proper place and open- 
ing into the combustion chamber. The valve stem 
passes through its guide and the valve spring is at- 
tached to the lower end of the stem. Pressing against 
the valve stem is the valve-lifter proper which, in 
turn, is pressed against by a small pivoted arm. In 
the center of the illustration and directly above the 
crankshaft of the engine is seen the valve operating 
cam. In this particular case, only the exhaust valve 
cam is shown but the inlet cam would be directly 
back of it. 

As the cam rotates, the valve will be allowed to 
remain closed until the projection of the cam comes 
underneath the lifter. The valve will then be opened 
and held open while the cam projection is passing 
underneath the lifter. After the cam has turned 
through a certain part of a revolution, the valve will 
be closed by its spring. The length of time during 
which the valve remains open is determined by the 
shape and size of the cam projection. The cam is 
positively driven by means of gearing or chains. More 
consideration will be given to this cam drive a little 
farther along. Details of the lifter device used with 
one V type engine are shown in Figure 25. 

VALVE LOCATION 

An examination of many of the engine illustrations 
in this and other chapters will show that both the 
inlet and exhaust valves are often mounted in a 
pocket-like projection formed at one side of the com- 
bustion chamber. This is known as the side-by-side 
location for valves. Other engines, for example, the 



56 THE MOTOR CYCLE HANDBOOK 

type shown in Figure 26, mount only the exhaust 
valve in the lower part of the combustion chamber 
pocket while the inlet valve is carried directly above 
the exhaust valve and in the top of the same pocket. 
In this latter design the inlet valve is operated by 




Figure 26. — Valve Mechanism of Harley-Davidson V-Type 

Engine. 

means of a valve-lifter which presses against a push 
rod. The push rod presses against one end of a valve 
rocker lever and the other end of this valve rocker 
lever presses down upon the end of the inlet valve 
stem and thus opens the valve. In the side-by-side 



THE MOTOR CYCLE ENGINE 



57 





Figure 27. — Gear and Cam Mounting- of Harley-Davidson 

Two-Cylinder Opposed Engine. The Cams With 

Their Large Driving Gear Are Seen 

Removed in the Lower Part of 

the Illustration. 



58 TIIK MOTOR CYClA'l HANDBOOK 

type of engine, both valves an; operated directly from 
their lifters with the use of the push rod and rocker. 
There is always a great deal of discussion as to the 
relative merits of these two types of design. Each 
one has certain undoubted advantages in its favor, 
but, like almost Everything else in mechanics, each 
has certain points against it. Jn actual practice, either 
type of design when well built, gives excellent results 
and the choice; between the two rests with the ideas 
of the designer as to the relative importance of the 
various advantages and disadvantages. Motor cycle 
engines have also been built with both of the valves 
mounted in the head but at the present time this 

practice is very much in the minority, the side-by-side 

cr side-and-head locations being used by almost all 
of the manufacturers. 

VALVE TIMINO 

Before describing the exact methods of timing the 
opening and closing of the valves in relation to the 
travel of the piston, it will be necessary to explain 
a few additional details about two of the strokes of 
the engine. The elementary principles governing the 
Strokes have already been briefly treated in an earlier 
portion of this chapter. 

Inlet Stroke. — The inlet stroke commences at or 
near the upper dead center position of the piston. 
Witfi the inlet valve open and the piston moving 
downward on the inlet stroke, the charge of fresh 
gas is drawn from the carburetor. When the piston 
reaches the bottom of its stroke the fresh gas is enter- 
ing the cylinder at a great rate of speed and this 
stream of gas has a considerable momentum. Even 



THE MOTOR CYCLE ENGINE 



59 




Figure 28. — Valve Operating- and Ignition Driving Gears in 
the Indian V-Type Engine. 



60 THE MOTOR CYCLE HANDBOOK 

with the piston at the bottom of its stroke, the cylinder 
has not been completely filled with gas because a par- 
tial vacuum has been produced by the rapid motion of 
the piston. The inrushing gas is tending to destroy 
this vacuum but if the inlet valve were to close as 
soon as the piston reached bottom center, the gas 
stream would be shut off and the cylinder would re r 
main only partly filled with fresh gas. In actual prac- 
tice the inlet valve does not close at lower dead center 
but is allowed to remain open until the piston has 
started upon the next upward stroke (compression 
stroke). Even with the piston traveling on the up- 
stroke the gas continues to enter the cylinder because 
of this momentum. 

Exhaust Stroke. — The maximum pressure of the 
burning gas is supposed to occur with the piston at 
its top center following the compression stroke. This 
pressure rises to a value of several hundred pounds 
to the square inch. As the piston passes down on 
the power stroke, the pressure becomes less and less 
but even with the piston at the bottom of the power 
stroke the pressure is still very high and if this high 
pressure were allowed to remain when the piston 
starts back on the exhaust stroke, it would mean that 
the engine would have to overcome so much back 
pressure that there would be a very considerable re- 
duction in the power output. In order to reduce this 
back pressure as much as possible the exhaust valve 
is opened before the piston reaches the bottom of the 
power stroke so that the gas may start to escape. The 
exhaust valve remains open through and to the end 
of the down stroke, all through the next upward 
stroke (exhaust) and in a great many engines the ex- 
haust valve remains open slightly after the upper 



THE MOTOR CYCLE ENGINE 61 

dead center following the exhaust stroke. This may 
allow the two valves to be open at the same time. 

It is not the general practice to allow the exhaust 
valve and the inlet valve to be open at the same time 
because the burning gas might possibly be forced 
back into the inlet pipe. Therefore, as the exhaust 
valve stays open slightly after the upper dead center 
following the exhaust stroke, and if the valves should 
not be open at the same time, it requires that the 
opening of the inlet valve be delayed until after this 
upper dead center. This delayed opening of the inlet 
valve has no great effect on the volume or quantity 
of fresh gas drawn into the cylinder because even 
were the inlet valve to remain closed until the piston 
had descended to a considerable distance, the vacuum 
that would thus be formed would simply serve to in- 
crease the speed of the incoming gas when the valve 
finally opened. 

Timing Gears. — In order to fix in the mind the re- 
lation between valve action and the position of the 
piston, the four strokes of the engine should be con- 
sidered. The first stroke is the inlet and the piston 
travels downward. The second is the compression 
with the piston traveling upward. This second stroke 
completes the first revolution of the crankshaft. The 
third stroke is the power or firing stroke with the 
piston moving downward and the fourth is the exhaust 
stroke with the piston moving upward. The third 
and fourth strokes complete the second revolution of 
the crankshaft during the complete cycle. Thus, for 
one cycle there are two revolutions of the crankshaft 
and four strokes of the piston. During the complete 
cycle of two revolutions the inlet valve opens once 
and the exhaust valve likewise opens once. Therefore, 



62 THE MOTOR CYCLE HANDBOOK 

in order to operate the valves at the correct time their 
cams must run at one-half the speed of the crankshaft 
so that each valve may be made to open during each 
second revolution. The connection between the crank- 
shaft and the camshaft is generally made by gears, as 
in Figure 28, and when it is thus made, the gear on 
the crankshaft has just one-half the number of teeth 
as has the gear on the camshaft. This relation of two 
to one allows the camshaft to run at one-half the speed 
of the crankshaft. The meshing of the gears with 
each other determines the exact point during the 
strokes at which the valves open and close. 

Timing ~by Degrees or Inches.— There are two meth- 
ods by which the position of the piston in its stroke 
may be described. One method consists of telling 
what fraction of an inch the piston has traveled from 
top center on the down stroke, or else of giving the 
fraction of an inch that the piston lacks of reaching 
the lower end of its stroke. The topmost position 
of the piston is called top center and the lowermost 
position is called bottom center. The exact position 
of the piston may be given as before or after top 
center or else before or after bottom center. 

The second method of telling the position of the 
piston is according to the degrees of a circle, the circle 
being considered as a revolution cf the crankshaft 
and generally being marked or measured on the rim 
of the flywheel. A complete circle contains 360 de- 
grees, and 360 degrees would therefore equal one 
revolution. A half circle, or 180 degrees, would equal 
one stroke. If the piston were half way down in its 
stroke it would have traveled 90 degrees and its posi- 
tion would then be given either as 90 degrees after 
top center or 90 degrees before bottom center. 



THE MOTOR CYCLE ENGINE 



63 



Valve timing positions are generally given in de- 
grees of the circle with reference either to top or bot- 
tom center. 

Inlet Valve Timing. — It has been stated that the 
inlet valve opens after the exhaust valve closes and 




Figure 29. — Valves Operated by Cams Carried on the Outside 

of an Internally Toothed Timing Gear 

(Iver-Johnson), 



this is true in most cases but there are many engines 
built in which the exhaust closing and inlet opening 
overlap one another. In this case the inlet valve opens 
before the exhaust valve has closed. The exact time 



64 THE MOTOR CYCLE HANDBOOK 

of opening the inlet valve really depends on the clos- 
ing of the exhaust valve more than on any other one 
factor. 

It has been shown that the inlet valve should remain 
open after bottom center in order to allow a full charge 
of gas to enter the cylinder. The point of closing the 
inlet varies between thirty and sixty degrees after 
bottom center following the inlet stroke, the exact 
point cf closing depending on factors such as the 
engine speed and the resistance to gas flow encoun- 
tered in the gas passages. 

Exhaust Valve Timing. — The exhaust valve closes 
anywhere from top dead center following the exhaust 
stroke up to as much as thirty degrees after top dead 
center. This closing point is dependent upon engine 
speed and various other factors. The higher the speed 
of the engine and the greater the difficulty of getting 
rid of the exhaust gas, the later will the exhaust 
valve close. 

The exhaust valve is opened anywhere from thirty 
to sixty degrees before bottom center. This, like the 
other valve-timing points, depends on the general 
design and speed of the engine. The earlier the ex- 
haust valve opens, the less will be the back pressure 
at the end of the exhaust stroke but too early opening 
would allow too much loss of the expanding gas and 
the net result would be a reduction in power. 

COMPRESSION RELEASE 

Motor cycle engines are put into motion either by 
means of a starting crank which is foot operated or 
by wheeling or pedaling the cycle. Because of the 
high compression that is used in a great many of these 






THE MOTOR CYCLE ENGINE 65 

engines, the cranking operation required in starting 
may be found quite difficult. In order to make these 
engines easy to crank, the compression is often re- 
lieved to a certain extent by means of lifting the 
valves part way from their seat or by providing a 
special relief valve. This device is called either the 
compression release or the valve lifter, the latter term 
being incorrect. 

In one typical design, the construction of the com- 
pression release is as follows: Between the two in- 
let valve rockers is a short shaft having a toothed 
segment near one end. This segment meshes with 
teeth cut on the circumference of a cam plate ; known 
as the exhaust valve relief cam. On the surface of 
the plate are formed cams which lift the exhaust valves 
through the rockers and valve-lifter when the plate is 
moved to a certain position. 

HORSEPOWER 

The actual power developed by any internal com- 
bustion engine can be accurately determined only by 
running tests. The results of such tests are generally 
plotted in the form of curves and are made available 
by a great many engine and motor cycle manufac- 
turers. 

The nominal horsepower is often calculated by 
means of some one or another of many different for- 
mulas. The most generally used horsepower formula 
is that which has been adopted by the Society of 
Automotive Engineers (S. A. E.). This formula was 
derived from the older one for horsepower in which 
were considered the mean effective pressure, the length 
of the stroke, the area of the piston head and the num- 



66 THE MOTOR CYCLE HANDBOOK 

ber of cylinders in the engine. In using this older 
formula it was generally difficult to arrive at the mean 
effective pressure without having indicator card data. 
In the S. A. E. formula, this factor is eliminated by 
assuming an average for this pressure. The factor 
of the length of stroke is also eliminated by assuming 
that the engine is running at a speed which causes the 
piston to travel a thousand feet per minute. 

The formula for S. A. E. horsepower of a four- 
cycle engine is as follows : 

HP: ^ 



2% 

In this formula, D stands for the diameter of the 
piston, which is generally called the bore of the engine 
or of the cylinder, and N stands for the number of 
cylinders. In arriving at the horsepower, the number 
representing the bore is squared ; that is, multiplied by 
itself, and this product is multiplied by the number 
of cylinders. The last product thus arrived at is 
divided by 2% and the quotient gives the horsepower. 
It is often stated that this formula does not take 
into account the length of stroke and that therefore 
it is inaccurate. This conclusion is incorrect because 
the S. A. E. formula assumes that the engine will be 
running at a piston speed of a thousand feet per 
minute. In order for an engine with a short stroke 
to reach this speed, its number cf revolutions per min- 
ute will have to be a great deal higher than the 
number of revolutions per minute of an engine having 
a longer stroke. For example : A thousand feet per 
minute equals twelve thousand inches per minute. If 
the stroke is three inches, one revolution or two strokes 
will make six inches travel, and twelve thousand 



THE MOTOR CYCLE ENGINE 67 

divided by six gives two thousand revolutions per 
minute as the speed at which this engine will develop 
its S. A. E. horsepower. If the stroke were only one- 
half as long, then the engine would have to go twice 
as fast to develop the same power. 

Displacement. — Engines are more easily compared 
according to their piston displacement than according 
to their S. A. E. horsepower because the piston dis- 
placement takes direct account of both the bore and 
the stroke but leaves speed out of consideration. 

The piston displacement is the volume of gas dis- 
placed when the piston moves from one end of its 
stroke all the w r ay to the other end. This volume is 
calculated by multiplying the area of the piston head 
by the length of the stroke. The following table gives 
the piston head areas of motor cycle engines. By mul- 
tiplying the proper area by the length of the stroke, 
the displacement may be determined. 

AREAS OF PISTON HEADS 





Area in 




Area in 




Area in 


Bore 


Square 


Bore 


Square 


Bore 


Square 


Diameter 


Inches 


Diameter 


Inches 


Diameter 


Inches 


n 


1.767 


n 


3.976 


3 


7.069 


1A 


1.917 


2* 


4.200 


3 T V 


7.366 


if 


2.074 


2f 


4.430 


H 


7.670 


1H 


2.237 


O 7 
^16 


4.666 


h\ 


7.980 


1^ 

L 4 


2.405 


2} 


4.909 


H 


8.296 


lit 


2.580 


9 9 


5.157 


3& 


8.618 


If 


2.761 


2f 


5.412 


3f 


8.946 


111 
i 16 


2.948 


m 


5.673 


3 T 7 <r 


9.281 


2 


3.142 


21 


5.940 


31 


9.621 


9 i 


3.341 


m 


6.213 






2i 


3.547 


2| 


6.492 






9-3 


3.758 


2if 


6.777 







c68 THE MOTOR CYCLE HANDBOOK 

TWO-CYCLE ENGINES 

With, the engines that have been described in the 
preceding pages, four strokes and two revolutions are 
required in order to complete the cycle which is neces- 
sary for the production of one power stroke. That 
type is called the four-stroke cycle or, more commonly, 
the four-cycle engine. 

There is another type of internal combustion engine 
properly called the two-stroke cycle but whose name 
is generally abbreviated with the words, two-cycle. 
This type of engine is in quite common use for light 
weight machines both as a built-in part of the motor 
cycle and as an attached power plant for a bicycle. 

In the two-cycle engine there are the four functions 
of inlet, compression, power, and exhaust, the same as 
in the four-cycle type, but all of the functions for one 
cycle are completed with two strokes of the crank 
shaft. This is made possible by utilizing a gas tight 
crankcase and performing a part of the compression 
in this crankcase. 

The most generally used type of two-cycle engine is 
the three-port design, and the action of a typical power 
plant of this kind may be understood by reference to 
Figures 30 to 34. The following explanation is 
adapted from the description given by the Cleveland 
Motor Cycle Manufacturing Co., and applies to their 
engine, but is equally descriptive of almost all two- 
cycle designs such as used in motor cycle practice. 

Eeferring to Figure 30, the parts are named as 
follows: A is the cylinder, B the piston, C the con- 
necting rod, D the piston pin, E the crank pin, F the 
flywheel, and G the air tight crankcase. At II is the 
inlet port or opening through which gas is admitted 



THE MOTOR CYCLE ENGINE 



69* 



to the engine. The exhaust port K, through which 
the burned gas escapes, is directly above it. By-pass 
L is a passage which connects the crankcase with the* 
cylinder through the transfer port M. R is the spark 
plug between the points of which the spark for ignit- 




Figure 30. — The Parts of a Two-Cycle Eng-ine (Cleveland). 



ing the gas takes place, and S is the compression 
release valve. 

Starting with the piston at the bottom of the cylin- 
der as shown by Figure 30, assume that the flywheel 



7Q 



THE MOTOR CYCLE HANDBOOK 



is being slowly turned, moving always in the same 
direction. As the flywheel turns, the piston, pushed 
up into the cylinder by the connecting rod, acts as an 



ie 




Figure 31.— Two-Cycle Engine With Piston Beginning to 

Uncover the Inlet Port. 

air pump. This creates a partial vacuum in the crank- 
case which, as previously mentioned, is air tight. As 
the piston moves up to the position shown in Figure 



THE MOTOR CYCLE ENGINE 71 

31, its lower edge begins to uncover the inlet port, 
leaving an opening through which the gas passes as 
it is drawn in by the vacuum in the crankcase. 
By the time the piston reaches the top of the cylin- 




Figure 32. — Two-Cycle Engine With Inlet Port Fully Open. 

der as in Figure 32 the inlet port is entirely uncov- 
ered and the engine has taken in a full charge of gas. 
Continued movement of the flywheel causes the con- 



72 



THE MOTOR CYCLE HANDBOOK 



necting rod to pull the piston back toward the lower 
end of the cylinder, closing the inlet port and pre- 
venting the escape of the gas which has just been 
drawn into the crankease. Further downward travel 



... 




Figure 33. — Two-Cycle Engine With Piston Beginning 
Uncover the Transfer Port. 



to 



of the piston compresses this gas, until in the position 
shown in Figure 33, the piston's upper edge begins 
to uncover the transfer port, allowing the compressed 






THE MOTOR CYCLE ENGINE 73 

gas to pass from the crankcase through the by-pass 
into the cylinder. 

When the piston reaches the bottom of the cylinder 
and is back in the position shown by Figure 30, the 
transfer port is wide open and the full charge of gas 
has passed from the crankcase to the cylinder. 

It will be noted that at this time the exhaust port 
is also wide open, and it might be expected that the 
incoming gas would pass directly over the piston and 
out of the exhaust port without doing any useful work. 
However, this is avoided by means of a projection or 
baffle plate on top of the piston, the object of which 
is to deflect the incoming gas toward the top of the 
cylinder and away from the open exhaust port. The 
position of this baffle with reference to the exhaust 
port is of great importance in the engine's operation. 

The piston now starts once more on its upward 
travel, closing the exhaust and transfer ports and 
again compressing the gas which is now in the cylin- 
der instead of in the crankcase. In the meantime 
another vacuum is being created in the crankcase and 
the inlet port opened to admit another charge of gas, 
exactly as was done during the first upward stroke. 
At the instant when the second upward stroke is 
completed and the piston is once more in the position 
shown by Figure 32, the compressed gas above it is 
ignited by a spark at the spark plug, driving the pis- 
ton down on its power stroke and at the same time 
compressing the fresh charge in the crankcase. Near- 
ing the end of this stroke the top of the piston uncov- 
ers the exhaust port as in Figure 34 and allows the 
burned gas to escape through the muffler and outlet 
pipe. 

Immediately after the opening of the exhaust port 



74 



THE MOTOR CYCLE HANDBOOK 



the transfer port is again opened to admit fresh gas 
as in Figure 33, thus completing the cycle of opera- 
tions which, after the motor is started, is repeated at 




Figure 34. — Two-Cycle Engine With Piston Beginning to 
Uncover Exhaust Port. 



every revolution of the flywheel or "two strokes" of 
the piston. The complete Cleveland power plant is 
shown in Figure 35. 



THE MOTOR CYCLE ENGINE 



75 



In some two-cycle designs, part of the gas which 
passes from the crankcase to the cylinder through the 
by-pass travels through openings cut through the wall 
of the piston, this being shown by the arrows in Fig- 




Figure 35. — Power Plant Using- Single-Cylinder Two-Cycle 
Engine (Cleveland). 

ure 36. In small two-cycle engines it is necessary to 
make the air space of the crank chamber quite lim- 
ited in volume in order to produce sufficient compres- 



76 



THE MOTOR CYCLE HANDBOOK 



sion pressure at this point. The construction of an 
engine having closely fitted parts in the crankcase is 
shown in Figure 37. 

Two-Cycle Oiling. — In the usual type of four-cycle 
engine the lubricating oil is carried to the crankcase 




Figure 36. — Flow of Gases Through Two-Cycle Engine 
Having Port Hole in the Piston (Precision). 



and this oil is splashed about by the connecting rod 
so that the bearings and the cylinder walls are lubri- 
cated. This scheme of oiling would not be practical 
in a two-cycle engine because such a quantity of the 



THE HOTOR CYCLE ENGINE 77 

lubricant mixed with the crankcase gas would have 
a detrimental effect on the mixture. Two-cycle engines 
are lubricated by mixing oil with the fuel in the fuel 
tank in such proportions that there are ten to sixteen 
parts of fuel to one part of oil. The manufacturers' 
instruction books specify the proportions which should 
be used and they also specify the grade or kind of oil 
which should be bought. 

It is quite possible that peculiar conditions of serv- 
ice will call for a variation from the oil proportion 
recommended. Hard, long or fast driving will require 
a greater amount of oil just as it would in a four-cycle 
engine and it may be best to increase the quantity. 
However, an excess of oil will produce greater carbon 
deposits and there may be some trouble expected with 
the spark plug and with clogging of the exhaust lines. 

It is never advisable to pour oil directly into the 
crankcase under ordinary service conditions. Neither 
is it well to attach drip oilers or force pumps. If the 
proportion of oil in the fuel is correct, the two-cycle 
engine will be properly lubricated without any addi- 
tional attention. 

If a two-cycle machine has remained idle for some 
length of time a little additional oil may be introduced 
into the engine by slowly pouring the oil into the air 
inlet of the carburetor just after the engine has been 
started. After the excess of smoke has disappeared 
the machine may be driven as usual. 

A side and a front section through a two-cycle 
engine are shown in Figures 38 and 39. In these illus- 
trations may be seen some of the details of a practical 
design. 

It is necessary that the oil be thoroughly mixed 
with the fuel in the main supply tank, for should there 



78 



THE MOTOR CYCLE HANDBOOK 



be any separation of the two liquids it is quite prob- 
able that the carburetor will become clogged. It is 
always best to mix the oil and the fuel in a separate 
can before pouring the mixture into the tank. Shake 
the mixture thoroughly and make sure that no oil 




Figure 37. — Close Fitting of Parts in a Two-Cycle 
Crankcase. 

remains unmixed in the bottom of the can. Should it 
be impossible to do this work in a separate receptacle, 
one-half of the fuel may be poured into the supply 
tank and oil then added. The liquids should be well 
shaken in the tank and the balance of the fuel finally 
added. The gasoline and oil will not separate after 
they are once properly mixed. 



THE MOTOR CYCLE ENGINE 



79 



Two-Cycle Horsepower. — For a given bore and 
stroke, the two-cycle engine will develop more power 
than will the four-cycle type. This is because the two- 




Figure 38. — Piston and Port Construction of Two-Cycle 
Engine (Schickel). 

cycle has twice as many power strokes in a given num- 
ber of revolutions as the four-cycle. 

From the above it might be assumed that a two- 
cycle engine of a given size would develop twice the 



80 THE MOTOR CYCLE HANDBOOK 

power of the corresponding four-cycle, but this is not 
the case, because the two-cycle is less efficient and does 
not use the fuel to such good advantage as does the 
four-cycle. The compression pressure cannot be car- 
ried as high in a two-cycle engine, the burned gas is 
not so thoroughly ejected from the cylinder, and there 
is a certain loss of fresh gas through the exhaust port. 

The generally accepted ratio between the two types 
of engine is that the two-cycle develops 1.65 times the 
power that is developed by a four-cycle of the same 
size. In order to arrive at the power of the two-cycle 
engine by means of a formula the following is used: 
The cylinder bore or diameter is squared ; that is, mul- 
tiplied by itself; the result is multiplied by the number 
of cylinders and the second result is divided by 1.515, 
when the quotient will give the horsepower of the 
engine. 

Two-Cycle Troubles. — There are some points about 
two-cycle engines which require special attention in 
order to secure satisfactory operation. One of the 
most necessary cautions to be observed is in keeping 
the spark plugs well cleaned, for they have a tendency 
to foul to a greater extent in the two-cycle engine than 
in a four-cycle type. 

The importance of maintaining a correct mixture 
of lubricating oil with the fuel has already been 
explained, and if this point is not attended to trouble 
of various kinds will surely result. If the proportions 
are incorrect or if the liquids are not well mixed the 
result may be hard starting, lack of power, overheat- 
ing, or knocking. 

A too rich mixture will cause the two-cycle engine 
to four-cycle ; that is, to fire only on each second revo- 
lution. If one of these engines fires regularly, but 



THE MOTOR CYCLE ENGINE 



81 




Figure 39. — End Section Shewing 1 Crankcase Construction 
of Schickel Engine. 



82 THE MOTOR CYCLE HANDBOOK 

less frequently than usual, and shows a tendency to 
emit considerable smoke even after warmed up it gen- 
erally indicates that the mixture is too rich in fuel 
and it should be made leaner. 

Carbon deposits do not affect the two-cycle engine 
as harmfully as they do the four-cycle because of the 
absence of poppet valves over which the exhaust gases 
pass. However, an excessive collection of carbon in 
the exhaust ports or in the muffler will cause a decided 
loss of power, and such deposits should be removed 
once in each two to five thousand miles of travel. 






CHAPTER III 
ENGINE OILING 

A great deal may be said about scientific or semi- 
scientific methods of determining the value and suit- 
ability of an oil for a certain engine. Farther along 
in this chapter these methods will be described; but, 
after all, there is one rule which, if followed, will 
obviate the necessity for such tests, and this rule is : 

Buy good oil, made and recommended by a well 
known refiner, and be sure that you get this kind of 
oil when you buy. 

Practically all oil makers publish charts of recom- 
mendations, and in one of these charts you will find the 
name and model of your motor cycle together with 
the grade of lubricant suitable for each season. 

It pays to buy good oil, because money saved here 
would be spent many times over on worn out engines. 
Good oil will wear itself out in lubricating, but with 
poor oil the wear will be on the engine itself. 

Whenever possible oil should be bought in original 
labeled cans or barrels ; or, if this is not possible, be 
sure of the origin of bulk oil that is bought openly 
by the measure. All grades of oils are produced by 
all kinds of makers and are sold through many chan- 
nels. Some are good and some are anything but good ; 
therefore, it pays to be careful and to insist on know- 
ing your oil and its origin. 

Requirements. — An engine oil must first of all pro- 

83 



84 THE MOTOR CYCLE HANDBOOK 

vide a film between the surfaces of moving parts, such 
as bearings and pistons. This film must keep these 
surfaces separated so that the wear will be of the oil 
and not of the parts. The oil is also depended upon 
to form a seal between the piston and the walls of the 
cylinder so that fresh, burning and spent gases may 
be kept above the pistons. 

In order to do these things satisfactorily the engine 
oil must spread easily over the surfaces, it must flow 
freely to the parts and cling tenaciously to them. Last 
of all, when the oil does get above the pistons and 
exposed to the inflamed gases it must burn clean and 
without leaving an excess of soot or carbon. A cer- 
tain oil may do all of these things in one engine, and 
yet fail in another because the suitability of the oil 
depends on the age and condition of the mechanism, 
on the type of construction and on the kind of oiling 
system that is used in the engine. 

The qualities of an oil which are generally spoken 
of are shown in the following list, arranged in the 
order of their importance: 

( 1 ) Viscosity, ' 6 thickness ' ' or ' ' body. ' ' 

(2) Flash point. 

(3) Freedom from acids and alkalies. 

(4) Specific gravity, "Baume test." 

(5) Cold test. 

(6) Carbon residue. 

(7) Fire point. 

(8) Color. 

Viscosity. — This quality determines the ability of 
the oil to flow freely at various temperatures and to 
a certain extent indicates its ability to form a satis- 
factory film for the bearings and an efficient piston 



ENGINE OILING 85 

seal. The viscosity of an oil varies greatly with its 
temperature, becoming less as the heat increases and 
generally being given, for purposes of comparison, at 
100° F., also in some cases at 200° to 212° F. and at 
60° to 70° F. The viscosity is given as the number 
of seconds required for a given quantity of oil to flow 
through a certain size opening at the temperature 
named. 

Flash Point. — This is the temperature at which the 
oil gives off an inflammable vapor which, upon presen- 
tation of a flame, will ignite or "flash," but which 
will not continue to burn. An oil having a high flash 
point does not vaporize in the crankcase and escape 
as quickly as one with a low flash. 

Freedom from Acids and Alkalies. — An engine oil 
should be "neutral" chemically; that is, have no 
remaining traces of either acids or alkalies which were 
used during the processes of refining, cleaning and 
bleaching. 

"When an acid or an alkali is heated, as it would be 
in the engine, it attacks the surfaces of shafts and 
bearings and rapidly pits and corrodes the valve faces 
and seats. 

The neutrality of any oil or grease may be tested 
by securing a supply of both red and blue litmus 
paper strips from a drug store. Immerse the paper 
in the oil being tested and if acid is present the blue 
paper will turn red, while if the oil contains free 
alkali the red paper will turn blue. 

Specific Gravity. — This measures the weight of a 
given volume of the oil when compared with the weight 
of an equal volume of water. It is measured in degrees 
on the "Baume" hydrometer scale and is usually taken 
at 60° F. The gravity of an oil has, in general, little 



86 THE MOTOR CYCLE HANDBOOK 

to do with its lubricating qualities. Pennsylvania and 
Eastern oils are of light weight and those from West- 
ern bases are heavier. 

Cold Test. — This is the temperature at which the 
oil becomes so thick from cold that it no longer flows 
readily. It has nothing to do with the lubricating 
qualities after the oil is once in use, but may be of 
value when sufficiently low in case the engine has 
much exposed piping in which the oil may congeal if 
exposed to outside temperatures. 

Practically all engine oils will thicken if exposed 
to a zero temperature and those which start to congeal 
at but little below freezing may make it difficult to 
crank an engine during the first start in winter 
weather. If it can be had without sacrificing other 
desirable qualities, a low cold test is an advantage. 

Carbon Residue. — If a sample of oil is heated and 
maintained hot until the part remaining becomes hard 
and like carbon, this remainder is called the carbon 
residue and is measured in proportion to its weight 
in comparison with the weight of the original sample. 

The carbon residue depends to a great extent on 
the viscosity of the oil and does not always indicate 
the amount of carbon that may be deposited in the 
engine because the conditions are not exactly similar. 

Fire Point. — The degree of heat at which the oil 
takes fire and burns with a steady flame is known as 
its fire point or fire test. It varies with the flash 
point and by itself is of little value because an oil of 
low flash point will burn quickly regardless of the 
fire test, and with a high flash test the fire test will 
be correspondingly high. 

Color. — The color of an oil before it is used in 
the engine or heated is of no value in indicating 



ENGINE OILING 87 

its quality because almost any shade of color may 
be secured by the necessary filtering and bleaching 
during the refining processes. 

Motor Cycle Oil Requirements. — Because of the 
exceedingly high temperature at which the motor 
cycle engine operates, it requires an oil that is 
different from the one used for automobile engine 
lubrication. Motor cycle oil must have a high 
flash and fire point. The flash point of oil should 
be 375° to 400° for cold weather and from 450° 
to 475° for warm weather. The fire point should 
be about 450° in cold weather and 525° in warm 
weather. 

The motor cycle engine is subjected to both 
extremes of temperature because of its being air- 
cooled. In hot weather this engine reaches a very 
high temperature while in cold weather the metal 
of the cylinders rapidly falls to the same heat as 
the atmosphere. This makes it necessary that motor 
cycle engine oil have a low cold test so that there 
will be little danger of congealing during winter 
weather. 

The motor cycle requires two different grades of 
oil, one an extra heavy body for warm weather 
use, and the other a heavy body for cold weather 
running. The viscosity at 210° F. would be about 
sixty for winter and one hundred for summer use. 
As a general rule, the manufacturers recommend that 
certain makes and grades of oil should be used in 
their machines and these recommendations should 
be followed. The mere fact that an oil at atmos- 
pheric temperature shows a heavy body does not 
necessarily indicate that it is suitable for motor 
cycle work because many of these oils were made 



88 THE MOTOR CYCLE HANDBOOK 

with the requirements of the water-cooled engine in 
mind and the automobile engine works at so much 
lower temperature that difficulty would be encount- 
ered. The normal temperature in the combustion 
chamber of the motor cycle engine is between 900° 
and 1000° F. 

When operating a motor cycle in an especially 
cold climate or when the outside temperature is 
very low, it may sometimes be found that the oil 
recommended for cold weather use becomes so 
thick that much difficulty is encountered in start- 
ing the engine, and overheating takes place because 
of too slow feeding. In such a case, the oil may 
he thinned sufficiently for use by adding a small 
amount of kerosene. Care should be exercised to 
use as little kerosene as will allow the engine to 
operate and in no case should the proportion 
exceed one pint of kerosene to each gallon of oil. 

OILING METHODS 

Almost all of the earlier designs of motor cycle 
engines used a plain splash oiling system. By this 
method a certain quantity of oil was placed in the 
crankcase, this quantity being sufficient to raise the 
level to a point at which the connecting rod would 
strike the oil bath at each revolution of the crankshaft. 
This action served not only to lubricate the connecting 
rod bearing but also to lubricate all the remaining 
hearings and the cylinder walls by means of the oil 
spray resulting from the splash. This method, with 
various modifications, is still used in a majority of 
motor cycle engines. 

The principal change in oiling systems is found in 



ENGINE OILING 



89 1 



the adoption of highly perfected mechanically driven 
pumps which maintain the correct supply of oil for 
the engine. With most of these systems the oil is sent 
either directly into the crankcase, into the timing 
gear case or else is forced first against the piston and 
the cylinder walls and then into the crankcase. One- 
method of distribution is shown in Figure 40. Some 




Figure 40. — Oil Distribution to Lower End of Piston in 
Norton Engine. 

of the splash systems are of the circulating type in 
which oil is pumped from the reservoir into the crank- 
case and is then allowed to drain back into the reser- 
voir to be once more circulated by the pump. 

In many engines the crankcase vacuum is used to 
assist in the operation of oiling. On the upward stroke 
of the pistons a vacuum is created in the cylinder 



90 THE MOTOR CYCLE HANDBOOK 

below the piston and in the crankcase. This vacuum 
is controlled by the operation of a breather valve which 
is oftentimes mechanically operated from the timing 
gears. This vacuum is used to draw the lubricating 
oil to the cylinder wails from the oil vapor that exists 
in the crankcase due to the movement of the connect- 
ing rods. Because of the direction of rotation of the 
connecting rods and flywheels, one cylinder of a V 
type engine would receive more oil than the other 
cylinder. To prevent this excess of oil, many engines 
are fitted with a baffle plate which partially closes the 
lower end of the cylinder where it opens into the 
crankcase. The baffle plate used for the cylinder 
which would receive the most oil almost completely 
covers the opening, leaving but little more room than 
required by the connecting rod. The baffle plate for 
the other cylinder is made with much larger openings. 

Some motor cycle engines are built to force oil 
directly to the principal bearings, that is, to the lower 
ends of the connecting rods and to the bearings of 
the crankshaft. This result is secured by drilling pas- 
sages through the crankshaft and forcing the oil under 
pressure through these passages from which it escapes 
into the bearings. The excess of oil from the bearings 
is thrown off by centrifugal force and serves to lubri- 
cate the cylinder walls, the pistons, and the piston 
pins. Such a hollow shaft method of oiling a four- 
cylinder engine is shown in Figure 41, and one for a 
single-cylinder type in Figure 42. 

The engine oil lubricates the valve actuating mech- 
anism consisting of the cams, the valve-lifters and the 
timing gears. This oil is also generally used for lubri- 
cating other gears contained in the crankcase, such as 
those used for driving the magneto. In some designs 



ENGINE OILING 



91 






•3 

o 



0> 






O 
o 



3 
X 



P 



- 




92 



THE MOTOR CYCLE HANDBOOK 



this oil is used even after escaping from the crankcase. 
In a typical design the operation is as follows: The 
oil in the motor case is subjected to a slight pressure, 



rsssSSSSSSSSSS 







Figiwe 42. — Drilled Crankshaft and Piston Pin of Levis 

Engine. 



which is relieved through the compression release valve 
as the piston commences to descend. The oil from the 
motor base then enters the timing-gear case and lubri- 
cates the gears and other working parts within it. The 
surplus oil passes out through the air relief tube arid 
oils the short drrve chain. 



ENGINE OILING 



93 




Figure 43. — Worm Gear Driven Plunger Oil Pump (Reading- 
Standard) . 



94 



THE MOTOR CYCLE HANDBOOK 
ENGINE DRIVEN PUMPS 



The majority of motor cycle lubrication systems 
make use of a plunger type of pump. One such design 




Figure 44. — Position of Oil Pump on V-Type Engine 
(Excelsior). 

is shown in Figure 43. The plunger is raised and 
lowered by a worm-driven eccentric shown at the right 
hand side of the illustration. As the plunger is 



ENGINE OILING 



05 




Figure 45. — Oil Pump Mounting on Indian Engine, 



'96 



THE MOTOR CYCLE HANDBOOK 



raised, it draws a charge of oil into its barrel through 
the pipe coming from the tank. Within this pipe 
is a ball check valve (not shown). Oil is not drawn 
from the lower pipe because the ball valve in that pipe 
is drawn closed by the receding plunger and is held 
closed by a small coiled spring. When the plunger 
descends, the ball check in the left-hand pipe is closed 
while the lower valve is forced open, thus discharging 
the oil into the lower pipe. The amount of oil feed 
is adjusted by changing the amount of travel given 
the plunger. 




Figure 46. — Cam Operated Plunger Oil Pump 
(Harley-Davidson). 

The location and adjustment of a plunger oil pump 
similar to the one just described is shown in Figure 
44, while a slightly different disposition of the parts 
in the plunger pump is shown in Figure 45. A plunger 
pump in which the piston is raised by means of a 
spiral cam and is returned by a coil spring upon its 
escapement from the cam is shown in Figure 46. 

A somewhat novel form of oil pump is shown in 
Figure 47. It is a plunger and cone revolved in a 
socket by a ratchet operated from the valve lifter. 
The spring operated plunger within the cone is with- 



engine: oiling 



97 



drawn by a cam surrounding the plunger, and when 
it slides off the cam the spring drives the plunger 
down, discharging the oil from the chamber into the 
crankcase. 

Pump Adjustment. — The exact method of changing 
the oil pump feed in different machines is best learned 
from the makers' instruction books. With the oil 




Figure 47. — The Iver-Johnson Oil Pump. 

pump once correctly set for service conditions, there 
should be little, if any, need for changing this adjust- 
ment Eintil the pump wears or until a decidedly dif- 
ferent grade of oil is adopted. Should it ever become 
necessary to use light weight oil, adjustment will prob- 
ably be needed because otherwise an excess of lubri- 
cation will be sent into the engine. There may be 



THE MOTOR CYCLE HANDBOOK 



some wear and leakage at ball check valves and it is 
advisable to replace the old balls with new ones once 
a year. 

It will be found that the use of a side car will call 
for a great volume of oil being fed to the engine. It 
will generally be found that the use of a side car will 
call for about one-third more oil than is needed by the 
same machine ridden only in solo work. 

If it is found that the oil level in the crankcase 
shows a persistent gain after a considerable amount 
of riding, it indicates that the pump is feeding too 




Figure 48. — Adjustments of Indian Oil Pump. 2 : Cap on 

End of Pump. 3 : Lock Screw. 4 : Plunger. 

5 : Vent Plug. 

much while if it is necessary to make frequent addi- 
tions by means of a hand pump, it indicates that the 
mechanical oiler is feeding too little. In either case 
an adjustment is called for. In making the oil pump 
adjustments do not change them more than a turn at 
a time and after doing this, tighten the locking devices, 
close the pump, and ride a sufficient number of miles 
to know whether the wrong conditions are being cor- 
rected. Typical oil pump adjustments are shown in 
Figures 48 and 49. 



ENGINE OILING 



9& 



Air Locks. — When, for any reason, there is a failure 
of the oil supply to a mechanically operated pump of 
the type generally used, the pump will become emptied 
of liquid and an air lock will be formed in the oil 
passages or pipes. After that, even with the oil sup- 




Figure 49. — Adjustment of Oil Pump on Indian Scout. 

1 : Cap on Side of Pump. 2 : Cap on Top of Pump. 

3 : Lock Screw. 4 : Plunger. 5 : Vent Plug. 

ply again reaching the pump, incorrect lubrication 
will follow until the air that has been trapped in the 
passages is allowed to escape. Most pumps are pro- 
vided with openings for use under such conditions. 
With the screws or plugs removed from these vent 



100 THE MOTOR CYCLE HANDBOOK 

openings and with a plentiful supply of oil in the 
reservoir, the pump should be allowed to operate until 
there is once more a free flow either into the crank- 
case or through the vents to the air. With the oil 
flowing freely the vents may be closed and any dis- 
connected pipes replaced. An air locked pump will 
often overfeed. 

HAND PUMPS 

Many machines are fitted with a hand operated 
plunger pump used either as a sole means for send- 
ing oil to the engine or as an auxiliary means in addi- 
tion to the engine operated pump. When the hand 
pump is fitted as an auxiliary it is used to sup- 
plement the power driven pump under conditions 
which the power pump would be unable to meet with- 
out a change in its adjustment. The hand pump is 
used when climbing long hills, when pulling through 
deep sand or mud and when using the low or inter- 
mediate gear ratio over any great distance. The hand 
pump is also used when the machine is being driven 
at high speeds for long distances, this generally apply- 
ing to speeds in excess of forty miles an hour. The 
attachment of a side car when the mechanical pump 
has been adjusted for solo work will call for frequent 
additions of oil made by the hand pump. 

If the hand pump is used as a sole means for giving 
oil to the engine, one pumpful for each ten to fifteen 
miles driving will generally be required. The rider 
will soon learn to gauge the distance that one pumpful 
of oil will carry the machine and will then be governed 
accordingly. In using the hand pump, the plunger 
should be drawn up quite slowly so that oil and not 
air will be drawn into the pump. The downward 



ENGINE OILING 101 

stroke should be made at a moderate speed and it 
should be steady from beginning to end. If the pump 
is operated too fast, it will draw more air than oil 
and the lubrication of the motor may be insufficient. 
In all cases it is advisable to give the engine about 
one-half pumpful at each injection and to do this twice 
as often as a full pump would be used. 

Hand oil pumps are sometimes built in such a way 
that the pump draws a charge of oil into a barrel from 
which the oil is fed to the engine by a drip feed, this 
drip feed being adjusted to give a certain number of 
drops per minute. With such an outfit, the drip feed 
adjustment may be set to suit the operating conditions. 
If solo running at ordinary speeds calls for a barrelf ul 
of oil each five miles, side car work would require a 
barrelful every four miles, and racing about every 
three miles. Three speed models require more oil 
than machines having but one gear ratio because of 
the extra running in low and intermediate with the 
three speed machine. When using a drip feed oiler 
care should be exercised to shut off the oil whenever 
the engine is idle even if it is only for a short time. 

OIL RENEWAL 

Because of the exceedingly poor grade of gasoline 
that is now available there is a certain portion of the 
fresh mixture that is not burned in the engine and 
that finds it way into the crankcase oil. This dilution 
of the oil destroys its body and lowers the flash point 
with the result that the engine loses compression and 
power while the fuel and oil consumption increase. 
If neglected, this condition soon results in worn cylin- 
ders, pistons, piston rings, shafts and bearings with 



102 THE MOTOR CYCLE HANDBOOK 

all the attendant troubles. Carbon deposit, both above 
the piston and in the crankcase, increases rapidly and 
the engine shows a general all-around poor condition. 

The trouble described may be prevented to a great 
extent by using a correct oil which will form a tight 
piston seal around the rings and by keeping the engine 
as warm as possible without overheating. The choker 
used while starting should not be kept closed for any 
longer than necessary to get the engine under way 
because this draws a charge rich in liquid 'fuel. 
Finally, and of the greatest importance, the oil should 
be drained from the crankcase and replaced with fresh 
at regular intervals. 

After a new machine has been driven four or five 
hundred miles, the oil should be drained; and, there- 
after, at the end of each thousand to fifteen hundred 
miles running, a similar procedure should be followed. 
Should the motor cycle be used for short trips with 
frequent starts and stops, or if it is used a great deal 
during cold weather, the draining should be done 
oftener than just mentioned. 

The drain plug or valve in the bottom of the crank- 
case should be opened and all of the oil allowed to 
run out. The opening should then be closed and gaso- 
line poured into the crankcase. The engine may then 
be cranked for about a minute in order to wash out 
the oiling system, and the gasoline then be drained 
as was the oil. 

After the gasoline has been completely drained, the 
oil level should be brought to its usual height by the 
addition of fresh lubricant. 

Such draining is essential during cold weather 
because of the fact that a certain amount of water 
results from the combustion of the gases and this 



ENGINE OILING 103 

water will quite likely settle in the crankcase where, 
even if it does not mix and emulsify w r ith the oil, it 
may possibly freeze. 



CHAPTER IV 

THE FUEL SYSTEM 

Parts of the motor cycle which are used to furnish 
a combustible gas to the engine cylinders include a 
fuel tank, an inlet manifold or pipe between the cylin- 
ders and the carburetor, the carburetor itself and the 
necessary feed pipes, valves and strainers, all of these 
being seen in Figure 50. 



FUEL 



Present day gasoline consists of a mixture havin; 
various characteristics of weight and evaporative qual- 
ities. Gasoline is described by mentioning its weight 
in relation to water according to degrees of the Baume 
scale, also its boiling points. Gasoline has an initial 
boiling point at which the first vapors are formed and 
a final boiling point at which the liquid is completely 
evaporated. 

The weight or gravity of the fuel does not mean a 
great deal as to its suitability for use in an automo- 
bile engine, this being true for reasons that will be 
explained. On the other hand the boiling points have 
a great deal to do with easy starting and general satis- 
factory performance. 

When the crude petroleum is distilled at the refin- 
ery, a number of products are secured. Among the 
most familiar are lubricating oils, kerosene and gaso- 

104 



,. 



THE FUEL SYSTEM 



105 



line. One of the chief differences between these three 
products, taken as examples, is in their weight or 
specific gravity. 

The weight of ' ' gasoline ' ' represents the average of 




Figure 50. — Carburetor Mounting" Between the Cylinders of 
V-Type Engine (Indian). 



the oils of which the fuel is composed. Thus, 76 
degree gasoline and 40 degree kerosene, in equal parts, 
would make a liquid which could be called 58 degree 
gasoline. 



106 THE MOTOR CYCLE HANDBOOK 

As everyone knows, kerosene is hard to burn in a 
gasoline engine, while good gasoline is easily burned. 
Inasmuch as the above mixture is in reality half kero- 
sene, that half will be difficult to burn. 

Gasoline is a physical mixture and not a chemical 
one. If a certain quantity of the liquid be exposed 
to the air it will, of course, evaporate. First the gaso- 
line will disappear leaving kerosene and oil, next the 
kerosene will disappear and only an oily deposit will 
be left. 

The initial boiling point is the temperature at which 
the gasoline starts to vaporize. It will be readily 
realized that the lower this temperature, the easier the 
fuel will ignite because the liquid must be vaporized 
before it will take fire. This initial boiling point varies 
between 125° and 200° F. Final boiling points run 
from 325° to 500°. 

In order to secure easy starting, smooth running, 
and comparative freedom from carbon deposits it is 
apparent that a low initial boiling point and a low 
final boiling point will be desirable. This is secured 
in good fuel, but in a blend composed of low grade 
kerosene and high grade gasoline, it cannot be secured. 
Such a blend would have the initial boiling point of 
the gasoline, which might be around 150°, but it would 
have an end boiling point like that of the kerosene 
which might be around 500° in actual practice. An 
initial boiling point of 125° to 150° and an end point 
of about 350° will give good results. 

The gasoline secured from filling stations and 
garages generally has a gravity not above 54°. It is 
also possible to secure high test fuel having a gravity 
between 60° and 64°. This high test gasoline not only 
facilitates starting but it has less tendency to dilute 



THE FUEL SYSTEM 107 

the lubricating oil in the engine crankcase. High 
test gasoline is more easily volatilized and ignites to 
make a more complete combustion and less unburned 
products than does the low-test fuel. At temperatures 
below 20° F., the low-test fuel will be difficult to ignite 
when the engine is cold, and below zero it will be 
practically impossible to ignite it for starting. 

In very warm weather, the high test fuel shows a 
considerable loss by evaporation in the carburetor and 
in the tanks, and it is therefore somewhat uneconomi- 
cal. Very light gasoline may even boil in the carbu- 
retor during hot weather. 

The tank is generally carried in the frame and just 
above the engine. It has an average capacity of 
between two and one-half and three gallons. The 
manifold is of simple construction with motor cycle 
engines ; in the single-cylinder V type twins consisting 
of only a short length of pipe, and in the four-cylin- 
der types showing little or no complication when com- 
pared with similar parts used for automobile engines. 
The pipes and valves require no special explanation. 
This leaves the carburetor as the principal and the 
most interesting part of the fuel system. 

CARBURETOR PRINCIPLES 

It is the purpose of the carburetor to transform the 
liquid fuel into a vapor or at least into a spray com- 
posed of very fine particles. It is the further purpose 
of this instrument to mix the fuel vapor with a quan- 
tity of air such as will produce a mixture which will 
give the desired power while burning. 

The low grade of fuel that is available has intro- 
duced many difficulties into the problem of carburetor 



108 



THE MOTOR CYCLE HANDBOOK 



design. On the first motor cycles the fuel mixture 
was produced by an arrangement called a mixing 
valve in which a jet of gasoline was allowed to enter 
a stream of incoming air. The gasoline of that day 
was so volatile and so highly inflammable that this 
simple arrangement gave good results. 

All of the modern carburetors include two principal 



N 



t 

1 



(?. 



H 



e^:ff= 



£ X 



Figure 51. — Elementary Parts of a Float Feed Carburetor. 

A: Air Inlet. C: Float Chamber. F: Float. 

L: Float Level. N: Nozzle. P: Fuel Pipe. 



parts in their make-up. One of these parts consists 
of a jet or opening through which comes the liquid 
fuel as it enters the air stream and this jet is enclosed 
within the air tube. The second part includes an auto- 
matic valve which is operated by a float in such a way 
that a fixed level of liquid fuel is maintained within 
the body of the carburetor. These elementary parts 



THE FUEL SYSTEM 109 

are shown in Figure 51. Referring to the illustration, 
liquid fuel comes from the supply tank through the 
pipe P. This liquid passes into the float chamber C 
through the float valve V. When the liquid has risen 
to a height called the float level, and indicated by the 
line L, the float F has risen high enough to cause the 
float valve to shut off the flow of incoming fuel. The 
liquid level has now risen to a point in the nozzle end 
which corresponds to the float level in the bowl. Out- 
side air is drawn in at the point A and travels through 
the air tube in the direction indicated by the arrows. 
The upper end of this tube is connected with the com- 
bustion chamber of the engine through the manifold 
and the inlet valve. Suction or partial vacuum created 
in the air tube by the descent of the piston on the 
inlet stroke causes a spray of liquid fuel to issue from 
the jet and to mix with the air stream. These parts 
would make up the simplest possible type of float feed 
carburetor. 

It is necessary that the proportions of the fuel mix- 
ture be practically unchanged over wide ranges of 
engine speed and the carburetor just described would 
not meet this condition. The jet opening could be 
proportioned in relation to the air tube to make a 
perfect mixture for one certain air velocity or engine 
speed. If the speed were to be either increased or 
decreased, then the proportions of fuel and air would 
undergo a decided change. With an increase of suc- 
tion the flow of fuel from the jet or nozzle would 
increase in a certain ratio but this same suction would 
not serve to increase the flow of air in the same ratio. 
The air would become thinner and the mixture would 
then be too rich in fuel. With a decrease in speed, 
the volume of air would not decrease as rapidly as 



HO THE MOTOR CYCLE HANDBOOK 

would the volume of fuel and the mixture would then 
become too weak for proper operation of the engine. 
There are three principal ways in which this difficulty 
may be overcome and these three ways allow all car- 
buretors to be placed in one of three classes, j 

i 

I AIR VALVE CARBURETORS 

The first class provides additional air at high speeds 
and reduces this additional air as the engine speed 
decreases. Such an instrument is shown in Figure 52. 
Referring to the upper drawing of this illustration, 
the air passage and the fuel nozzle may be seen in 
the center of the carburetor. The upper end of the 
nozzle is fitted with an adjustable needle valve which 
serves to regulate the flow of fuel from the nozzle. 
Referring to the lower left-hand drawing, the float 
may be seen surrounding the central air passage and 
the float valve which closes the fuel inlet is shown 
at the right of the carburetor. Again referring to the 
upper drawing, it will be seen that after the incoming 
air has passed around the nozzle and taken up a sup- 
ply of fuel spray, this air passes to an upper chamber 
and thence through a throttle valve at the right into 
the inlet manifold of the engine. At the left-hand 
side of this upper chamber is a valve called the aux- 
iliary air valve. This valve opens inwardly under suc- 
tion and is normally held on its seat by the coiled 
spring which is clearly shown. The tension of this 
air valve spring may be adjusted by the thumb screw 
shown at the extreme left. 

As the speed of the engine increases, the flow of 
liquid fuel is rapidly increased in volume while the 
flow of air around the nozzle does not increase to such 



THE FUEL SYSTEM 



111 




Figure 52. — Construction of Breeze Motor Cycle Carburetor. 



112 THE MOTOR CYCLE HANDBOOK 

an extent. The mixture therefore, requires additional 
air. The same suction that increases the fuel flow 
serves to draw the auxiliary air valve away from its 
seat and the required amount of air is admitted 
through this valve and mixes with the volume of air 
and fuel coming from around the spray nozzle. 

The carburetor just described has two adjustments ; 
one for the auxiliary air and the other for the amount 
of fuel passing through the nozzle. The fuel adjust- 
ment is by means of the needle valve which partially 
closes the upper end of the nozzle. This fuel adjust- 
ment is generally used for regulating the mixture at 
low engine speeds while the auxiliary air valve adjust- 
ment is used for securing a correct mixture at high 
engine speeds. 

One of the best known carburetors employing an 
auxiliary air valve is shown in Figure 53. A section 
through the air valve alone is shown in the lower left- 
hand drawing, the valve being indicated by A and a 
special manual adjustment by 12. This carburetor 
embodies a unique feature in that the fuel needle valve 
is moved by movement of the throttle so that as the 
throttle is opened more and more to admit a greater 
volume of mixture to the engine cylinders, the needle 
valve is raised farther and farther from its seat in 
the upper end of the nozzle, thus admitting more fuel 
to the mixture. The needle valve is raised and low- 
ered by a pivoted lever one end of which surrounds 
the valve stem while the other end rests against a cam 
operated with the throttle. The contour of this cam 
is changed by the adjustment shown in the upper 
left-hand drawing and indicated by Z. 

To adjust this carburetor for low speed, see that the 
leather air valve A seats lightly; then turn knurled 



THE FUEL SYSTEM 



113 



button / to the right until the needle E seats in the 
spray nozzle, cutting off the flow of gasoline. Now 
turn I to the left about three turns and open the low 
speed air adjusting screw L about three turns. Then 
open the throttle about half way to start the engine. 




I 


J t — m 






jkj-j. 


F 




11 f=Sifr®L 








J 




W^ 





















-H 



Figure 53. — Construction and Adjustments of Schebler Model 
H Carburetor. 



After starting the engine, close the throttle and turn 
the needle valve adjusting screw / to the right until 
the mixture becomes so lean that the engine backfires 
or misses. Then turn the adjusting knurl I to the left, 
notch by notch, until the engine runs smoothly. If 
the engine runs too fast with this low speed adjust- 



Ill THE Motor CYCLE HANDBOOK 

ment, turn the low speed adjusting screw L to the 
right, 

Tho carburetor is now ready for the high speed 
adjustment and the throttle and spark should be 
advanced. The adjustment is now made by the pointer 
Z which, as it moves from 1 to 3, increases the supply 
of gasoline. Moving the indicator from 3 to 1 cuts 
down the flow of gasoline. When the indicator reaches 
the right point, the engine will run without missing 
or backfiring, [f, when lever Z is turned to 3, the 
mixture is still too lean, and causes the engine to 
backfire, increase the tension of the air valve spring 
by turning the air valve adjusting screw 12 to the 
left. The high speed air valve on the side of the car- 
buretor is to be used only for extreme high speed. 
This valve should be kept closed when adjusting the 
carburetor. 

The air valve can be locked in a closed position 
which materially helps in easy starting. It operates 
by pulling out the knurled button 12, and giving it 
one-quarter turn. When the engine is started, turn 
the button 12 back. This releases the air valve A 
and allows it to operate in the customary manner. The 
locking feature of the air valve does not in any way 
alter Ihe instructions for adjustment of the air valve. 
When first starting the engine, if it backfires on 
account of being cold, do not readjust the carburetor 
but wait until the engine warms up. 

PLAIN TUBE CARBURETORS 

In the second class of carburetors there is no aux- 
iliary air valve nor are there valves of any other kind 
except for the throttle which controls the volume of 



THE FUEL SYSTEM 



115 



p 



X 



CD 



■eT" 



r==?3: 



V 



A 



L 



'mm* 



■a 



It 




Figure 54. — Operating- Principle of the Zenith Carburetor. 



116 THE MOTOR CYCLE HANDBOOK 

mixture sent to the engine. This is known as the plain 
tube type carburetor. One of the best known exam- 
ples is shown in Figures 54 and 55. 

The principle upon which the Zenith carburetor 
operates may be understood by reference to Figure 
55. The elementary type of carburetor shown at the 
top in Figure 54 consists of a single jet or spraying 
nozzle placed in the path of the incoming air and fed 
from a float feed device. While it might be supposed 
that, with increase of engine speed, the flow of both 
gasoline and air would increase in proportion, this is 
not actually the case. The flow of gasoline increases 
in almost direct proportion to the engine speed but 
because the increase of suction or vacuum tends to 
draw the air out thinner and thinner, the actual quan- 
tity of air does not increase in any such proportion 
and the mixture of gas supplied by such a carburetor 
would become richer as the speed increases. 

Referring to the center drawing Figure 54 it will 
be seen that, between the float bowl and the jet, has 
been placed a well J which is open to the outside air 
and through which the gasoline passes by way of the 
opening I, thence passing as before to the jet H. It 
will be realized that the maximum amount of fuel that 
can reach the jet II will be determined by the size of 
the opening I without regard to the suction existing 
around H because the flow through I is not directly 
acted upon by this suction. With such a device the 
air flow will increase with speed of the engine; and 
while it will not be in direct proportion, there will be 
an increase over the whole range of engine speed. 
Now, inasmuch as the flow of gasoline cannot increase 
beyond a certain amount, while the flow of air will 
increase, the mixture furnished by such an arrange- 



THE FUEL SYSTEM 



117 



merit will become weaker with increase of engine 
speed. 

In the Zenith carburetor these two types of jets 
are combined as shown in the lower drawing. The 
direct suction, or richer mixture type, leads through 
pipe E and nozzle G, while the limited flow device 




Figure 55. — Construction of Zenith Carburetor. 



consists of the well J, opening I, passage K and jet H. 
As the flow of fuel from jet H counteracts the change 
in the flow from jet G, the complete mixture may be 
made practically of constant proportions over all 
ranges of speed. 

There are four variables used in making the initial 
adjustment of a Zenith carburetor. One of these is 
the choke tube which is the passage surrounding the 
jets. Another is the main jet which controls the flow 
of fuel at high speeds. A third is the idling jet which 
in Figure 55 is shown just at the left of the main jet. 
The fourth adjustment is the idling well which con- 
trols the air flow at low engine speeds. With these 



118 



THE MOTOR CYCLE HANDBOOK 



four adjustments once determined for an engine they 
are put into place in the carburetor and remain there 
without change or alteration. 

MANUAL CONTROL CARBURETORS 

In the third class of carburetors, the additional air 
required at high engine speeds is controlled by means 




Figure 56. — Construction of Schebler Model AL Carburetor. 

of a manually operated valve. This means that there 
are two carburetor controls within reach of the rider. 
One of these controls is for the throttle while the 
other is for the extra air. 

One such carburetor is illustrated in Figure 56. 
This instrument is made with a two-piece piston throt- 
tle, one being used as a throttle and the other as an air 
choke for starting and warming up the engine. 



THE FUEL SYSTEM 



111) 



To make an adjustment, first turn on the main 
needle on the top of the carburetor three or four turns ; 
then open the low speed needle on the bottom of the 
carburetor about one and one-quarter turns from its 
closed position. 




Figure 57. — B. S. A. Carburetor Shown With Throttle and 

Air Control Wide Open at the Top and With Both 

Controls Nearly Closed at the Bottom. 

Start the engine by flushing the float bowl and 
after the engine has become thoroughly warmed up, 
adjust the main or high speed needle on the top of 



120 



THE MOTOR CYCLE HANDBOOK 



the instrument, cutting down the fuel supply until 
the engine backfires. Then turn on a little more gas 
a notch at a time until the engine runs smoothly and 
the proper adjustment will have been secured for 
high speed. Next adjust the low speed needle, located 
at the bottom of the carburetor, until the desired low 







Figure 58. — Construction of B. & B. Carburetor, Showing 
Throttle and Air Controls. 

speed is secured. No further adjustments are required. 
Another example of the third class of carburetors 
is shown in Figure 57. It will be noted that the whole 
of the air under all conditions is drawn across the jet. 
The air and throttle valves are in effect two cylinders 
with through ports bored so that when the two valves 






THE FUEL SYSTEM 121 

are fully open they virtually constitute a tubular pas- 
sage from air inlet to engine. 

The upper drawing shows the valves fully opened, 
in which position the carburetor presents no obstruc- 
tion to the free passage of the mixture. The lower 
drawing shows the valves partly closed. It will be 
noted that the air is drawn down and directly across 
the jet, then upwards through the throttle to the 
engine. At all speeds the engine suction is concen- 
trated across the jet. 

In operating such a carburetor as just shown, the 
air valve is closed for starting and is then opened 
sufficiently to secure a good running mixture. More 
power is secured while running by either gradually 
reducing the air opening or gradually increasing the 
throttle opening. The jet opening is adjusted by a 
needle valve shown in the center of the carburetor. 

Still another type of the third class of carburetor 
is shown in Figure 58. Referring to the illustration, 
it will be seen that this carburetor is adapted for a 
double lever control, one lever of which controls the 
throttle and the other the air valve. The construction 
of the throttle is such that when opening it, it also 
opens sixty per cent of the total available amount of 
air, so that the maximum amount of extra air that is 
under control by the air valve only amounts to forty 
per cent instead of the usual hundred per cent. To 
the throttle valve is attached a needle which works 
in the jet so that as the throttle is raised or lowered, 
the needle is likewise raised or lowered. 

The needle is compound in shape, the first portion 
being parallel and after a certain distance becoming 
tapered, which taper continues to the end of the 
needle. The jet in which the needle slides is situated 



122 



THE MOTOR CYCLE HANDBOOK 



in a small choke tube admitting an amount of air suffi- 
cient to break up the gasoline as it issues from the 
orifice. Fitted in the throttle and completely enclos- 
ing the top of the choke tube is a cap into which the 
gasoline spray and air pass from the jet and choke. 
This cap is provided on one side with many holes of 
small diameter through which the gasoline and air 
have to pass. In Figure 59 is shown the float con- 
struction used with the carburetor just described. 




Figure 59.— Float Mechanism of B. & B. Carburetor. 



TROUBLES WITH THE FUEL SYSTEM 

Extreme, cold weather may make the operation of 
starting an air-cooled engine quite difficult. Under 
such conditions it is advisable to inject a small quan- 
tity of gasoline directly into the cylinders through 
pet cocks or through the spark plug openings. The 
engine can then be cranked with the pet cocks open. 
The gasoline frees the congealed oil and the engine 
can be cranked rapidly enough to obtain a good start- 



THE FUEL, SYSTEM 123 

ing spark. As soon as the engine commences to fire, 
the pet cocks can be closed. 

While it is possible to control the speed and power 
of the engine by means of the compression release, 
this is not good practice because with the exhaust valve 
raised in this manner, hot gases are continually flowing 
over the valve face and seat and this will cause rapid 
pitting and burning. 

It will often be found that long continued riding 
at high speed will cause the engine to apparently lose 
a great deal of its power, this effect being due to insuf- 
ficient lubrication. Better action will be secured if 
the throttle is partially closed for an instant once 
every mile or two. This closing of the throttle pro- 
duces a high vacuum in the cylinders and this vacuum 
assists in bringing an additional supply of oil up 
over the cylinder walls. 

Among the troubles which may be found in the car- 
buretor and which are not due to an incorrect adjust- 
ment are the following: Dirt or water may have 
entered the float bowl, or the strainer at the fuel 
inlet may have become clogged. The connection 
between the float and the float valve may have become 
bent so that the level of fuel in bowl is either too 
high or too low. The float itself may have become 
punctured if made of metal or it may be fuel soaked 
if made of cork. In either case the fuel level will 
be too high and the mixture will be too rich. Should 
benzol be used in a cork float carburetor the float 
should be covered with collodion because the benzol 
will dissolve shellac. It may also be found that the 
float or the float valve will stick in certain positions 
or that dirt may have lodged between the valve and 
its seat. 



124 THE MOTOR CYCLE HANDBOOK 

The spray nozzle may be clogged with dirt or some 
foreign material may have lodged between the nozzle 
opening and the adjusting needle valve. In some cases 
the throttle may be loose on its shaft or the controls 
may have loosened so that the throttle does not open 
and close properly. It is also possible that the stop 
screw which prevents complete closing of the throttle 
is not properly set. With an old carburetor there may 
be a considerable leakage of air past the throttle shaft 
openings. 

In carburetors using a choke valve of the butterfly 
type by means of which incoming air is shut off while 
starting, it may be found that the choker does not 
close tightly enough or that it does not remain fully 
open when released. Continued cranking with the 
choke closed or excessive priming of the cylinders with 
liquid fuel may act to prevent starting. The air valve 
should be examined to see that its springs are not 
broken and that the valve stem does not bind in any 
position. Any bending or jamming of the air valve 
will prevent the carburetor from furnishing a correct 
mixture and if the air valve stem or its guide have 
become very much worn, the mixture will be too weak 
at low speed. 

Difficulty will be encountered at low speeds should 
the inlet manifold or its fastenings become loose. If 
gaskets are used they must be clean and whole. A 
failure of fuel at the carburetor may result from a 
stoppage of the yent through the filler cap of the 
fuel tank because it is necessary that air flow into 
the tank in order that fuel may flow out of it. Any 
dirt or other obstructions in the fuel tank, in the out- 
let valve, or in the pipe to the carburetor will result 
in a poor mixture at high speeds. 



CHAPTEK V 
MAGNETO IGNITION 

Two types of ignition are in use. One of these types, 
which will be described in this chapter, uses a magneto 
for the source of current while the other type, to be 
described in the following chapter, uses the lighting 
dynamo and a storage battery as sources of current. 

A magneto ignition system as shown in Figure 60 
includes the magneto itself, the necessary wiring con- 
nections and the spark plugs in each of the cylinders 
of the engine. 

In order to produce a spark within the cylinder of 
the engine it is necessary that the electric current 
jump across a small gap in the spark plug which is 
inside the cylinder and surrounded by the gaseous 
mixture. A current of extremely high pressure or 
voltage is required in order to pass across this gap 
because the resistance of the mixture is so great that 
no ordinary voltage has any effect. The pressure of 
the current from either of the primary sources used 
for ignition is never more than from six to fifty volts, 
but this current of low voltage is of comparatively 
great volume or amperage, and is used to produce 
another current having voltage sufficiently high to 
pass across the gap. through the mixture, and in so 
doing produce the heat of the electric spark. The 
required high voltage or high tension current is 

125 



126 



THE MOTOR CYCLE HANDBOOK 




MAGNETO IGNITION 



127 



secured by induction from the primary current of low 
voltage. 

It has been found that any change in the strength 
of a magnetic field within which is a coil of wire will 
cause electric currents to be induced in the coil, the 
strength of these currents depending on the intensity 
of the magnetism, and on its degree of change. 




SOi/fiCE 



Figure 61. — Principle of the Induction Coil. 

When a current of low voltage is passed through 
the primary winding of an induction coil as in Figure 
61 there is a current generated in the secondary wind- 
ing, but this current which is induced by completion 
of the primary circuit is not of sufficient strength to 
cause a spark in a cylinder. When, however, the cir- 
cuit through the primary winding is broken and the 
current ceases to flow, there is a very powerful action 
in the coil and a high tension current is induced in 
the secondary winding with sufficient voltage to cause 
the current to pass across the spark gap and ignite the 
mixture. 

THE BREAKER 



It has been explained that the greatest voltage is 
secured from an induction coil at the instant the pri- 



128 THE MOTOR CYCLE HANDBOOK 

mary circuit is broken. That part of the ignition 
mechanism which causes this break is called the con- 
tact breaker, circuit breaker or interrupter. A typical 
breaker is shown in Figure 62. 




Figure 62. — Breaker of the C. A. V. Mag-neto. 

The principal parts of the breaker include two con- 
tact pieces through which the primary circuit for the 
induction coil passes while these contacts are touching 
each other. When separated, the contacts prevent a 
further flow of this primary current. In connection 
with the contacts, or as, they are often called, the con- 
tact points or simply the points, there is a cam which 



MAGNETO IGNITION 129 

causes their separation at the instant a spark is desired 
in one of the engine cylinders. All of the remaining 
parts of the breaker are for the purpose of allowing 
the contacts and the cam to operate properly. 

One of the contact points is stationary while the 
other is movable. The stationary contact is securely 
mounted on the body of the breaker and is the member 
provided with means for changing the distance 
between the points when separated, that is, the sta- 
tionary contact is adjustable. The other contact is 
moved to open and close the circuit and is not 
adjustable. 

It is necessary that the contact points separate a 
certain distance from each other when the circuit is 
opened by the breaker, this distance usually being in 
the neighborhood of fifteen to twenty thousandths of 
an inch. 

The time at which the spark passes at the gap in 
the plug is determined by the instant at w T hich the 
breaker contacts separate and at which the resulting 
reaction takes place in the induction coil. 

This instant at which ignition is effected is an 
important point in the cycle of operations through 
which the internal combustion engine passes. It is 
at some time during the compression stroke, or at the 
end of this stroke, that the gas must be ignited. The 
exact instant at which the spark occurs depends on 
several factors but in all cases the object sought is 
that the entire charge will be fully aflame and at the 
point of greatest pressure when the piston has reached 
the top of its stroke and is ready to descend on the 
power stroke. 

The ignition flame starts in the gas immediately sur- 
rounding the spark and finally reaches the farthest 



130 



THE MOTOR CYCLE HANDBOOK 



points of the combustion space in the cylinder. Dur- 
ing this time of flame travel, the piston of the engine 
is moving with greater or less rapidity up or down in 
the cylinder, the piston speed depending on the imm^ 
ber of revolutions that the crankshaft is then making 
in a given length of time. In order that the engine 
may develop the greatest possible power from the 




Figure 63. — The C. A. V. Magneto. 

amount of fuel being used it is necessary that the gas 
be ignited at such time as will insure maximum pres- 
sure immediately after the piston starts on its down 
stroke. 

In order to cause the electric spark to pass through 
the inflammable mixture at such time as to produce 



MAGNETO IGNITION 131 

complete ignition of the charge when required, a 
majority of systems provide means for altering this 
time of breaker action to correspond with engine 
speed. 

THE CONDENSER 

It has been explained that the change of magnetism 
in the core of the coil which takes place upon breaking 
the primary current causes a flow of current in the 
secondary winding of the coil and this same change 
of magnetism produces a flow of current in the pri- 
mary winding as well. This induced flow caused by 
breaking the current at the points is of much greater 
voltage than the primary current itself and tends to 
continue to flow between the contacts as they open, 
thus causing an arc or hot spark. 

A device called a condenser is incorporated in the 
ignition apparatus for the purpose of collecting the 
induced current, preventing its causing a destructive 
arc at the contacts and also allowing the pow r er of 
the induced current to be returned to the coil in such 
a way that the change of magnetism affecting the sec- 
ondary winding is greatly increased and the resulting 
current in the secondary circuit is raised in voltage 
to produce a spark much hotter than would other- 
wise be secured. 

The condenser consists, in the form usually 
employed, of a number of strips of tin foil separated 
by insulators such as oiled or paraffined paper or cloth. 
Mica also is used in some cases as the insulator. Alter- 
nate strips of the tin foil are attached to each other 
so that one-half the total number of strips connects 
with one terminal of the condenser while the remain- 
ing half connects with the other terminal. This 



132 THE MOTOR CYCLE HANDBOOK 

arrangement provides a large surface of an electri- 
cal conductor (tin foil) separated by very thin layers 
of insulating material, which is in this case, called 
the dielectric. 

THE MAGNETO 

A magneto is a form of dynamo-electric machine 
especially adapted for the production of current suit- 
able for ignition but not suited for the production 
of a current that will charge a storage battery. The 
current from a magneto is alternating, and periodi- 
cally changes its direction of flow; while from a 
dynamo, the flow is direct and does not reverse its 
travel. The magneto has its fields formed by perma- 
nent magnets. Its current of comparatively low volt- 
age is changed to a high tension current by means of 
an induction coil carried in the magneto. 

The type of magneto known as the true high tension 
carries a secondary winding on the magneto armature 
together with the primary winding. The primary 
armature winding then acts as the primary of the 
combination which is, in effect, an induction coil, and 
produces changes of magnetism in the common core. 
These changes induce the high voltage impulses in 
the fine wire secondary winding. 

The principle upon which a magneto of the arma- 
ture type generates current may be understood by 
reference to Figure 64. The parts shown at A include 
the horseshoe shaped permanent magnet M to whose 
extremities are attached the extensions P-P called pole 
pieces. The inner faces of these pole pieces are curved 
and between them rotates the iron core B on the mag- 
neto drive shaft. On the core is carried a coil of wire 
C and it is in this wire that the current flow is induced. 



MAGNETO IGNITION 



133 



The coil and its core are parts of the magneto's 
armature. 

With the armature in the position shown at A in 
the illustration the magnetic lines of force from the 
magnet poles flow from the positive to the negative 
side,taking the path indicated by the arrows through 




Figure 64. — Rise and Fall of Voltage With Rotation of 
Magneto Armature Coil. 



the center of the coil. As the magneto shaft is rotated, 
the core and coil nnally assume the position shown 
at B. The lines of force still flow through the core, 
but because of the lessened surface presented to the 
face of the pole pieces, the flow has become smaller. 
Further rotation brings the parts to the position shown 
at C. Between B and C, the flow of magnetism 
through the coil stopped and again commenced, but 



134 THE MOTOR CYCLE HANDBOOK 

now in the opposite direction through the core and 
the coil wire. Between these last two points there 
has been an abrupt change in the intensity of magne- 
tism acting on the coil, in fact a complete reversal has 
taken place. At the end of a half revolution a second 
reversal takes place as the core once more assumes 
a midway position between the pole pieces and for 
each complete revolution of the armature there are 
two abrupt changes of magnetic flow through the 
core and coil. The rise and fall of the voltage is 
shown by the curve in the lower part of the 
illustration. 

The construction of a typical high tension magneto 
of the single-cylinder type may be understood by an 
examination of Figure 65. The beginning of the 
armature primary circuit is in metallic contact with 
the armature core, and the end of the armature pri- 
mary circuit is connected by means of the breaker 
fastening screw to the insulated contact block sup- 
porting the long contact on the breaker. The breaker 
arm carrying a short platinum contact is mounted on 
the breaker base, which in turn is electrically con- 
nected to the armature core. The primary circuit 
is completed whenever the two contacts are brought 
together and interrupted whenever these contacts are 
separated. The separation of the contacts is controlled 
by the action of the breaker arm as it bears against 
the steel cam or segment secured to the inner surface 
of the breaker housing. 

The high tension current is generated in the sec- 
ondary circuit only when there is an interruption of 
the primary circuit, the spark being produced at the 
instant the breaker contacts separate. The armature 
secondary circuit is a continuation of tbe arir^fure 



MAGNETO IGNITION 



135 



primary circuit, the beginning of the secondary being 
connected to the primary while the end of the second- 
ary is connected to the insulated current collector ring, 
or slip ring, mounted on the armature just inside the 
driving shaft end plate of the magneto. 

THE DISTRIBUTOR 

In the four-cycle engine each cylinder fires once for 
each two revolutions of the flywheel. A single- 



8RUSH 
HOLOGR 




GROUND 



GROUND 



Figure 65. — Low Tension and High Tension Circuits of 
Single-Cylinder Magneto (Bosch). 

cylinder engine would therefore require one spark 
which would call for one separation of the breaker 
contacts every second revolution of the flywheel. A 
two-cylinder engine would require twice as many 
sparks, or one for each revolution of the flywheel. 
Four cylinders call for two sparks each flywheel 
revolution. 

All of the sparks produced by the magneto are 
caused by the action of one pair of breaker contacts 



136 THE MOTOR CYCLE HANDBOOK 

and it will be evident that some means will be neces- 
sary to send successive sparks to different cylinders 
of any engine other than a single-cylinder type. The 
device which sends the current to the proper cylinder 
is called the distributor. 

The distributor receives the flow of secondary or 
high tension current from the fine wire winding of 
the armature coil and directs this flow of current into 
the wire leading to the spark plug in the cylinder 
which is then ready to fire, that is, to the cylinder 
whose piston is at the upper end of its compression 
stroke and ready to descend on the power stroke. 

In the single-cylinder magneto, no separate dis- 
tributor is required, as the high tension current from 
the armature secondary circuit is passed by the slip 
ring to a single brush, which is supported by a brush 
holder at the side of the shaft end of the magneto. 
A high tension cable between the brush holder termi- 
nal and the spark plug in the cylinder completes the 
secondary circuit. 

Two-cylinder magnetos often use a double ring to 
which the two ends of the secondary winding are led. 
High tension current for one of the cylinders is taken 
from one ring while the other ring supplies the remain- 
ing cylinder. Such a construction is shown in Fig- 
ure 60. 

The four-cylinder distributor consists of an insulat- 
ing cap or head in which are secured the terminals 
to which spark plug wires attach. Inside of the cap 
is a revolving member called the rotor which receives 
the high tension current from the coil, and by moving 
from point to point around the cap, carries this cur- 
rent to segments or pins which are in electrical con- 
nection with the spark plug wires. 



MAGNETO IGNITION 



137 



The distributor of this type is mounted above the 
breaker but with both breaker and distributor rotating 
in the same plane as shown in Figure 66. In this type 
of equipment the breaker cam has only half the num- 
ber of lobes as there are cylinders to be fired and the 
distributor rotates at one-half the breaker speed. The 
driving connection between the two parts is secured 
by a gear carrying the distributor rotor meshing with 




Figure 66. — Distributor Drive for Four-Cylinder Magneto. 

C: Central Contact. G: Driving- Gears. R: Rotor. 

S : Segment Attached to Spark Plug Wire. 

a pinion half the size of this gear and mounted on 
the breaker shaft. 

Two distinct types of distributor construction are 
in use. One type called the wipe contact, provides 
carbon or metal brushes in the distributor rotor or 
the cap, or in both rotor and cap, which complete the 
connection for the high tension current. The other 



138 THE MOTOR CYCLE HANDBOOK 

type, called a jump spark distributor, leaves a minute 
air gap between the current carrying member of the 
rotor and the connection for the spark plug cable ter- 
minal, the secondary current jumping across this air 
gap for each discharge of high tension current. 



SPARK PLUGS 






The spark plug is a device designed to carry the 
high tension current into the combustion space of the 
engine and to allow the current to form an arc or 
spark between two points separated by a definite gap, 
the heat of this spark causing ignition of the fuel mix- 
ture to take place. The spark plug must operate under 
the difficult conditions of extreme variations in tem- 
perature and pressure while at the same time pre- 
venting the improper escape of an electric current of 
thousands of volts pressure. 

In its simplest form the spark plug consists of a 
shell threaded on its outside surface so that it screws 
into some part of the combustion space wall, and inside 
of this shell an insulating bushing through which 
passes a conductor called the central electrode and 
through which the secondary current enters the com- 
bustion space. These parts of the plug are shown in 
Figure 67. 

The distance apart of the points in the spark plug 
is of great importance in properly firing the mixture. 
With a magneto as the source of ignition current the 
spark is comparatively weak at low speeds and becomes 
stronger and better able to jump the gap as the engine 
speed and magneto voltage increases. 

For average conditions and in the average engine 
the distance between the electrode ends, or the spark 



MAGNETO IGNITION 



139 



plug gap, should be between twenty-five and thirty 
thousandths of an inch. With magneto ignition, low 
speed missing calls for a smaller gap and high speed 
missing for a larger gap. 




CMTft/lL ELECTRODE* 
I/l/Si/LflTOft- 
J HELL 




Figure 67. — Top: Parts of a Spark Plug". Center: Section 

Through Splitdorf Spark Plug With Mica Insulation. 

Bottom : Section of A. C. One-Piece Spark Plug. 

The setting of the spark plug electrodes is an impor- 
tant function which is usually overlooked, w^ith the 



140 



THE MOTOR CYCLE HANDBOOK 



result that the magneto is blamed when it is not at 
fault. The setting of the spark plug electrodes should 
seldom exceed a gap of .025 of an inch to obtain the 
best results. Nothing is gained by a larger gap as it 
only imposes an extra strain on the magneto. This has 





Figure 68. — Left: One-Piece Spark Plug-. Right: Two-Piece 
or Separable Spark Plug-. 

been demonstrated by practical experience, both in 
touring and racing. If the engine does not fire evenly 
in both cylinders and a spark plug is suspected or 
skips in one cylinder, it is advisable to reverse the 
plugs, that is, place the suspected plug in the other 



MAGNETO IGNITION 141 

cylinder and should it continue to skip, the spark ping 
should be cleaned or replaced by a new one. 

Two-piece plugs may be easily cleaned by removing 
the bushing and the core from the shell and brushing 
the core with an old tooth brush dipped in gasoline. 
When the carbon deposit on the core is very heavy it 
may be scraped clean with a knife. Sometimes a spark 
plug is tested by holding it against the cylinder while 
sparking. This is not proof that the spark plug is 
in good condition as a plug will often spark in the 
open air but not when subjected to the compression 
of the engine. 

The ends of the spark plug electrodes should be 
cleaned from time to time with a piece of emery paper, 
as it has been found that the gasoline and oil sold 
in some localities will leave a deposit on the electrodes 
of the plug. This increases the resistance of the elec- 
trodes and will not permit the spark to pass freely 
from one electrode to the otljer. While inspecting 
the plug, the gap should be regulated, bearing in mind 
that a small gap makes easy starting but that an ordi- 
narily wide gap gives better all-around results. 

Should it be necessary to use a mica spark plug that 
has become badly oil soaked, most of the oil may be 
removed by means of heat. The core of the plug 
should be removed and held in the flame of a blow- 
torch for some length of time, at least until the 
appearance of burning oil has disappeared. 

Spark plugs can be more easily inserted and with- 
drawn if the threads are covered with graphite or a 
graphite paste. A cold plug should never be screwed 
into a hot engine because the contraction of the hot 
cylinder walls onto the cool plug will make the two 
parts into practically one piece. 



142 



THE MOTOR CYCLE HANDBOOK 






The insulating core through which passes the cen- 
tral electrode may be permanently fastened into the 
spark plug shell, in which case the plug is of the 
non-separable or solid type, or else the core may be 
held in place by means of a packing nut and gaskets 
so that the center assembly is easily removable for 
cleaning or replacement. This latter type is called 




Figure 69. — Spark Plug- Wire Attachment on Single-Cylinder 
Bosch Magneto. 

a separable or two-piece plug. Both constructions are 
shown in Figure 68. 

In Figures 69 and 70 are shown methods of attach- 
ing the spark plug wires to the magneto and the con- 
nection between the end of the wire and the brush 
that collects high tension current from the armature. 
Figure 69 shows the entire cover plate of the magneto 
and shows the carbon brush extending downward to 



MAGNETO IGNITION 143 

meet the collector ring. Figure 70 shows a brush 
holder that attaches at one side of the magneto. 

MAGNETO SETTING AND CARE 

Magnetos are often driven by means of a flexible 
direct connected coupling on a shaft intended for 
the purpose. As the magneto must be driven at a 
high speed, a coupling of some flexibility is preferable. 




Figure 70. — Spark Plug- Wire Attachment on Twin-Cylinder 
Bosch Magneto. 

A small inaccuracy in the lining up of the magneto 
with the driving shaft will be taken care of by the 
flexible coupling, whereas with a perfectly rigid 
coupling, the lineup of the magneto must be abso- 
lutely accurate. With the flexible coupling the vibra- 
tion of the engine will not be as fully transmitted to 
the armature shaft of the magneto as in case a rigid 
coupling is used. 



144 THE MOTOR CYCLE HANDBOOK 

Another method of driving the magneto is by means 
of a gear keyed to the armature shaft. Where this 
method of driving is employed, great care must be 
exercised in providing sufficient clearance between the 
gear on the magneto and the driving gear. If there 
should be a tight spot between these two gears it will 
react disadvantageously on the magneto. The third 
available method is to drive the magneto by means 
of a chain. Wherever gear or chain drive is used, 
precautions must be made against oil working into 
the magneto from the case containing the gears or 
the chain. 

Berling Magnetos. — To set the magneto, the piston 
in some one cylinder of the engine should be brought 
to the point on the compression stroke where the 
extremely advanced spark is desired to occur. The 
location of this point will vary somewhat in different 
makes of engines, but in the majority of cases it will 
be found to be somewhere between 3/8 inch and 3/16 
inch before the piston reaches top-center on its com- 
pression stroke. This position can be accurately deter- 
mined by removing either the inlet valve or the spark 
plug and bearing on the top surface of the piston 
with a wire or stick. By rocking the engine slowly 
backward and forward, the exact top-center position 
of the compression stroke can be determined by watch- 
ing the highest position of the wire or stick. Now turn 
the engine backward until the wire or stick drops the 
desired amount of advance for the engine in question. 
Next move the timing lever as far as possible in the 
direction opposite to the direction of rotation of the 
magneto. With the timing lever in this position, turn 
the magneto armature in the direction of the rotation 
until the contacts on the breaker just begin to open. 



MAGNETO IGNITION 



145 



The gear or coupling which was left loose for this pur- 
pose should now be tightened, thus rigidly fixing the 
relation between the piston of the engine and the mag- 
neto armature. With this setting the spark will occur 




Figure 71. — Breaker Construction of Berling- Magneto. 

in the front cylinder at the proper time. The breaker 
is shown in Figure 71. 

If the setting of the magneto and its connection 
to the engine have been carefully made according to 
these instructions, and the engine nevertheless should 
not give the maximum power, it is possible that the 



146 THE MOTOR CYCLE HANDBOOK ' 

amount of extreme advance of the piston has not been 
correctly chosen and it will be necessary to reset the 
magneto, using a different amount of advance. 

The setting of the magneto on a two-cylinder engine 
firing at 180 degrees is the same as that for the V 
type and may be made from either cylinder, care being 
exercised that the cam corresponding to the terminal 
attached to the plug in the cylinder being used is 
correct, otherwise the spark will occur on the exhaust 
stroke. 

The timing range of the magneto is twenty-five 
degrees, and with the setting as above described the 
spark may be made to occur several degrees after the 
piston passes top-center for starting or low speed 
running. 

With the fiber lever in the center of one of the 
embossed cams, the opening between the contacts 
should be not less than .016 inch and not more than 
.020 inch. The gage riveted to the adjusting wrench 
should barely be able to pass between the contacts 
when fully open. 

The contacts must be smooth and if pitting is in 
evidence, the surfaces should be smoothed off with a 
very fine file. When in the closed position the con- 
tacts should come into proper relation with each other 
over their entire surfaces. 

When inspecting the breaker, make sure that the 
ground brush in the back of its base is making good 
contact with the surface on which it rubs. 

There is provided on the cam housing cover a 
grounding spring and terminal. This terminal should 
be connected to a simple grounding switch for cutting 
out the ignition. This is a low tension connection 
so that it is not necessary to use high-tension cable. 



MAGNETO IGNITION 



147 



Lubricate the cams in the cam housing and the two 
rubbing surfaces of the fibre lever with a thin film 
of vaseline for every fifty hours of actual running. 
After the magneto has been ijistalled put ten drops 
of clean light cylinder oil in each oil cup and repeat 




Figure 72. — Section Through Berlins Magneto. 

this every thousand miles of actual running. Never 
use oil in the breaker and pay particular attention to 
prevent oil or other lubricant from reaching the 
contacts. 



148 THE MOTOR CYCLE HANDBOOK 

Bosch Magnetos.— To time the magneto to the 
engine, the crankshaft or flywheel is rotated to bring 
the piston to within one-quarter inch of top dead 
center on the compression stroke, and is maintained 
in that position. The magneto is then secured to the 
engine with the points of the breaker in the act of 
separating, the breaker housing being fully advanced. 

Rotating the housing in the direction opposite rota- 
tion, as indicated by an arrow on the oil well cover, 
gives the advanced position. 

The engine may be started and will operate with 
this timing, but if the engine characteristics are such 
that full power is not secured, the setting must be 
changed to bring the spark earlier in the piston stroke. 

In timing a magneto on a twin-cylinder engine as 
shown in Figure 60 the operation is similar. The 
piston of cylinder number one is brought to within one- 
quarter inch of top dead center of the compression 
stroke and maintained in that position. The magneto 
is then to be secured to the engine with the points 
in the act of separating, the breaker lever coming into 
contact with the steel segment bearing the mark I, 
the spark control lever being in full advance position. 

When the breaker lever is acted on by segment 7, 
the spark that is produced will pass to carbon brush 
7; this carbon brush is to be connected to the spark 
plug of cylinder number one. Carbon brush 77 is 
then to be connected to the second cylinder. 

If these settings do not develop the desired power 
output, the magneto is to be advanced slightly in rela- 
tion to the crankshaft, the spark thus being produced 
when the piston is more than one-quarter inch from 
top dead center to the compression stroke. It will be 
found that in general the spark should occur at a 



MAGNETO IGNITION 



149 



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150 THE MOTOR CYCLE HANDBOOK 

point in the stroke from one-quarter to five-eighths of 
an inch from top dead center. 

The only care required by the magneto is the oiling 
of the bearings, each of which should be given not more 
than four or five drops every five hundred miles. The 
breaker lever is intended to operate without lubrica- 
tion. Oil on the points will prevent good contact and 
will cause sparking and burning as well as an engine 
miss, therefore, great care should be exercised to pre- 
vent the entrance of oil to these parts. The correct gap 
between the breaker contacts when separated is .014 
of an inch. 

Dixie Magnetos. — The principle of operation may 
be understood by reference to Figure 74. The mag- 
neto consists, in its principal parts, of a set of mag- 
nets, a rotating member, a special field structure 
carrying the coils, the coil windings, a breaker, and a 
condenser. 

The rotating member, or rotor, consists of two 
revolving wings N and S, shown at 1 in the illustra- 
tion, which are separated by a bronze center piece. 
These wings are carried by the magneto drive shaft 
and revolve between the poles of the magnets, one 
rotor revolving adjacent to the North pole while the 
other revolves close to the South pole. Because each 
rotor always revolves close to its own pole of the 
magnets it always maintains the same magnetic polar- 
ity, one always being positive while the other is always 
negative. 

Again viewing a section of the magneto and looking 
across the magnets as in 2, 3 and 4 of Figure 74, in 
place of through the arch as in i, it will be seen that 
the rotor is enclosed by the lower ends of an arched 
field structure, on the upper part of which are placed 



MAGNETO IGNITION 



151 



the coil windings. As the rotor revolves it causes the 
magnetic lines of force to be changed about so that 
the magnetism flows back and forth through the field 
structure and the core of the windings, first in one 
direction, then in the other, according to the position 
of the rotor in relation to the poles of the field 
structure. 

Still referring to Figure 74 it wi 1 ! be seen that, by 




}ffllh 





Fig-ure 74. — Operating- Principle of the Dixie Magneto. 

rotating the wings very close to the ends of the mag- 
nets, they are in effect the rotating poles of the mag- 
net. At right angles to the rotating pole pieces or 
wings is the field structure consisting of laminated 
pole pieces F and G carrying across their top the 
windings TT. "When N is opposite G the lines of force 
flow from one pole X of the magnet to G and through 
the core C and F as shown in 2 of the illustration. 



152 THE MOTOR CYCLE HANDBOOK 

As shown at 3, the pole N has moved over to F and 
the direction in which the lines of force flow is reversed 
through the core and windings, now passing from F 
through C and G. At 4 in the illustration the rotating 
pieces occupy a position midway between the two fore- 
going so that the field pieces F and G are magnetically 
short circuited and all the lines of force are removed 
from the core C. 

Facilities for oiling are provided by an oil hole on 
the side of the instrument and ten drops of light oil 
every five hundred miles are sufficient. Before oiling, 
it is advisable to clean the oil hole of dust and grit. 
The breaker lever bearing should be lubricated with 
a few drops of light oil applied with a tooth pick 
every five hundred miles. The proper distance between 
the contact points when separated should be .020 inch. 

Whenever the wires leading from the magneto are 
taken off make sure that they are properly replaced. 
On a magneto of right hand rotation as shown by the 
arrow on the back plate cap, the terminal marked 
No. 1 always leads to the cylinder which fires first and 
which is usually the rear cylinder. 

Should it become necessary to clean the collector 
spool, remove the three screws holding the brush 
holder support and take the brush holder off, being 
careful not to damage the rubber gasket or ring. 

The collector spool may be cleaned with a piece of 
cloth dipped in gasoline and wrapped around the 
eraser end of a lead pencil. This is inserted in the 
hole of the housing, at the same time rotating the 
magneto by turning the motor over a few times to 
insure thorough cleaning. 

The carbon brushes in the brush holders should 
be free and project about one-quarter of an inch from 



MAGNETO IGNITION 153 

the end of the holder. Do not pull out the carbon 
brushes. 

For timing a single-cylinder engine, rotate the crank- 
shaft or flywheel so as to bring the piston to the upper 
dead center of the compression stroke. With the tim- 
ing lever fully retarded, the points of the breaker 
should be about to separate. For engines of the twin- 
cylinder type, rotate the crankshaft so as to bring 
the piston of No. 1 cylinder, which is usually the 
rear one (the first in direction of rotation) to the 
upper dead center of the compression stroke. With 
the timing lever in the full retard position, the points 
of the breaker should be about to separate when the 
fibre bumper of the breaker bar begins to ride on the 
nose of the cam marked No. 1. Some engines may 
require an earlier setting to obtain the best results. 

Simms Magneto. — To time the magneto, crank until 
cylinder number one is on top dead center with valves 
closed (beginning of working stroke, with connect- 
ing rod swung over on downward stroke side). 
Remove the breaker cover and distributor cap. Turn 
the magneto armature in the direction it must run 
until the contacts are just opening with the timing- 
lever in the fully retarded position (the retarded posi- 
tion is obtained by pushing the timing lever down in 
the same direction as the magneto armature rotates). 
The distributor carbon brush must at the same time 
be in a position to touch the distributor segment serv- 
ing cylinder number one. The driving gear or 
coupling should then be secure^ tightened on the 
magneto armature driving shaft, using the key in 
the keyway provided in the shaft. The magneto can 
now be coupled to the engine, care being taken not to 
change the foregoing adjustments. 



154 THE MOTOR CYCLE HANDBOOK 

It must always be remembered that the distributor 
brush rotates in the opposite direction to the armature, 
and that number two terminal on the distributor does 
not necessarily lead to number two cylinder, but to 
the cylinder firing; after that to which number one 
wire is led. The same applies to number three and 
number four terminals and cylinders. 

Any advance or retard desired in addition to that 
to be obtained by the variation of the timing lever 
must be secured on the engine alone by advancing 
or retarding the engine timing gears, but in no case 
should the setting of the magneto distributor or inter- 
nal armature gears be changed, as these have a cer- 
tain fixed relation to each other. Different settings 
of these two gears will seriously impair the efficiency 
of the magneto. 

The magneto should be oiled every two weeks or 
one thousand miles run with four or five drops of 
light machine (not cylinder) oil in each of the oil 
holes which are located over the armature driving 
shaft and near the top of the distributor. The breaker 
should never be oiled ; it may cause serious difficulty if 
oil is allowed to remain on it. 

The points should be set so as to open on each cam 
about one sixty-fourth of an inch, or the thickness of 
the gage on the wrench furnished. These points should 
be kept clean and free frcm oil, and should make 
even contact with one another over their entire sur- 
face. The breaker lever should pivot freely in the 
bushing. The breaker should be inspected occasion- 
ally and freed of dirt and oil. Only if it should 
become absolutely necessary should the platinum 
points be filed, and then only with a very fine flat file 
and by using great care. 



MAGNETO IGNITION 



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156 THE MOTOR CYCLE HANDBOOK 

MAGNETO AND IGNITION TROUBLES 

It is almost invariably the case that ignition trouble 
is due to a defective or dirty spark plug. It should 
be remembered that as the spark will have a tendency 
to burn the metal of the electrodes, the gap will 
gradually increase in size through use. The spark 
plug should therefore be examined occasionally for 
assurance that the gap is not too great. 

The magneto breaker lever should move on its 
pivot with sufficient freedom and the points should 
be so adjusted that they are separated. When the 
adjustment is made, great care should be taken to 
set the lock nut firmly in position. If the lock nut 
backs off it may cause serious injury to the parts. 

It is very rarely that difficulty is encountered with 
the magneto and suspicion should not be placed on 
the magneto until all other sources of trouble have 
been investigated. If the magneto is suspected, the 
first thing to do is to determine if it will deliver a 
spark. To determine this, disconnect one of the high- 
tensicn leads from a spark plug in one of the cylin- 
ders and place it so that there is approximately one- 
sixteenth of an inch between the terminal and the 
cylinder frame. 

Open the pet cocks on the other cylinders to pre- 
vent the engine from firing and crank the engine until 
the piston is approaching the end of the compression 
stroke in the cylinder from which the cable has been 
removed. Set the magneto in the retarded position 
and rapidly rock the engine over the top-center posi- 
tion, observing closely if a spark occurs between the 
end of the high-tension cable and the frame. 

If no spark is observed, then the trouble is in the 



MAGNETO IGNITION 157 

magneto. If a spark is observed the spark plugs 
should be investigated. To do this, disconnect the 
cables and remove the spark plugs. Then reconnect 
the cables to the plugs and place them so that the 
shells of the plugs are in metallic connection with, 
the frame of the engine. Then crank the engine, 
thus revolving the magneto armature, and see if a 
spark is produced at the spark gaps of the plugs. 

If the magneto and spark plugs are in good condi- 
tion and the engine does not run satisfactorily, the 
setting should be verified according to instructions 
previously given and, if necessary, readjusted to give 
correct timing. 

When attaching a magneto to a V type twin- 
cylinder engine it should be remembered that some 
of these engines have their cylinders set at an angle 
of 42°, others at 45°, and still others have an opening 
as great as 90°. It is not possible to use a 42° mag- 
neto on a 45° engine nor is it possible to make any 
other combination unless the units are designed to 
operate together. It is also important to know that 
the magneto is designed for the direction of rotation 
in which it will be driven. 

Among the commonly encountered magneto troubles 
are the following : The breaker contacts may be dirty, 
their gap may be incorrect, the contacts may be loose, 
or the breaker arm may be sticking. The contacts 
may sometimes be badly out of line with each other 
or one or more parts of the breaker may have worked 
loose. Some of the small brushes about the armature 
or breaker may have become broken or may be stick- 
ing in their holders. 

The distributor should be examined to see that 
it is not wet or dirty. The collector ring should be 



158 THE MOTOR CYCLE HANDBOOK 

kept clean and the safety spark cap should be free 
from accumulations of oil and dirt. 

If the magneto has been taken apart it may be 
found that the magnets have been replaced in the 
wrong position, that is, with part of the positive poles 
on one side and part of them on the opposite side of 
the armature. Careless handling of the magnets may 
have caused them to loose their strength. If the 
magneto drive is badly worn or loose or if the arma- 
ture bearings in the magneto are loose, it will be diffi- 
cult if not impossible to secure a satisfactory spark. 

The spark plugs will give trouble if the insulator 
is dirty either inside of the shell or on the part exposed 
outside the engine. The insulator may be broken if 
of porcelain or oil-soaked if of mica, and either type 
may be loose in the shell. The points of the plug 
between which the spark is supposed to pass may be 
touching each other or may be short circuited by oil 
or carbon. These points may have been burned away 
until the gap is too great or they may have worked 
loose, either in the core or in the shell. A plug should 
be of the correct length for the engine with which it 
is used, that is, it should not be so short that it will 
be pocketed and reached only by dead gases, neither 
should it be so long that there is danger of the plug 
end being struck by the valves or piston of the engine. 
The wiring should be examined to see that it is not 
short circuited or accidentally grounded by moisture, 
oil, or dirt. The insulation should be examined to 
see that it is not broken or chaffed especially at points 
of support. It may sometimes be found that the wire 
strands have become broken underneath the insula- 
tion. 

As a general rule, the spark should be carried as 



MAGNETO IGNITION 159 

far advanced as possible while running, this advance 
being just short of the point at which knocking is 
caused. The spark advance should generally be in 
proportion to the speed of the engine regardless of 
the power being developed. The engine should never 
be operated for any length of time with the spark 
retarded. When starting the engine with magneto 
ignition it may sometimes be necessary to advance the 
ignition almost all the way but with battery ignition 
a one-third to one-half advance will be sufficient if 
the timing is correct. 

A great many magnetos are driven by means of a 
chain and it is important that this chain be kept at 
the correct tension. Should the tension be too great 
there will be a grinding noise while the engine is 
slowing down with the compression release open. If 
the chain is too loose it will rattle. Unless the mag- 
neto drive chain is enclosed and automatically lubri- 
cated it will be treated in the same way as a driving 
chain, that is, cleaned and lubricated with a graphite 
grease preparation. 



CHAPTER VI 

DYNAMO LIGHTING AND IGNITION 
THE STORAGE BATTERY 

A storage battery for motor cycle use is made up 
of three storage cells. Each cell contains two kinds 
of plates, positive and negative, made from compounds 
of lead and immersed in a liquid composed of sul- 
phuric acid and water. A chemical action takes place 
between the plates and the liquid and the result of 
this chemical action is a flow of electricity through 
wires that are attached to the battery terminals. The 
battery does not store, and does not contain electricity, 
but is capable of generating a flow of current because 
of the action that takes place in the battery. 

In order to bring the elements of the battery into 
such condition that they will cause a flow of current, 
it is first necessary to send a flow of electricity through 
the battery. The energy of this current being sent 
through the battery is consumed in making one series 
of chemical changes and when outside circuits are 
connected to the battery, these changes take place in 
a reverse order and most of the energy absorbed from 
the flow of charging current is given back into the 
circuit to do useful work. The parts of a motor cycle 
hattery may be seen in Figure 76. 

The plates are made up of a metal framework called 
the "grid," and a paste called the active material 

160 



DYNAMO LIGHTING AND IGNITION 161 




Figure 76. — Parts of the Wico Motor Cycle Battery. 



162 



THE MOTOR CYCLE HANDBOOK 



is used to fill the spaces in the grid. Adjacent plates 
are prevented from touching each other by the use of 
insulators placed between them. The jar in which 
the plates, insulators and liquid are carried is made 




Figure 77. — Construction of Battery Grid. 



from insulating material that resists the action of the 
acid in the liquid. A grid is shown in Figure 77. 

The active material is made from lead oxides com- 
bined with other materials to give hardness and tough- 



DYNAMO LIGHTING AND IGNITION 



163 



ness and to make the plates porous so that the liquid 
can act on the material. The spaces between the bars 
of the grid are filled with this paste. The cell contains 
one more negative than positive plates and they are 
placed alternately so that both outside plates are nega- 
ive. This arrangement is shown in Figure 78. 

All the positive plates are joined together and all 




Figure 78. — Positive and Negative Plates Alternating- in a 
Battery Cell. 



of the negatives are similarly fastened together with 
connecting straps. The positive connecting strap is 
attached to the positive terminal of the cell, while 
the negative strap is fastened to the negative terminal. 
The groups thus formed, together with an insulator, 
are shown in Figure 79. 

A flow 7 of electric current sent through the cells 
causes a change in the material of the plates and the 
positives turn to peroxide of lead while the negatives 
turn to sponge lead. When the material in the grids 



164 



THE MOTOR CYCLE HANDBOOK 



has been completely transformed the battery is 
charged. 

The voltage obtained from one cell does not depend 
on the size or weight of the cell. The normal voltage 






Figure 79. — Positive and Negative Groups, Connecting- Straps, 
itid Insulator. 

under operating conditions is two for the cell, although 
this voltage varies slightly with the state of charge 
of the battery. When the material in the plates has 
been completely changed to peroxide of lead and 
lead sponge and the cell is still being charged, the 
voltage may be as high as 2.5, while with the battery 
discharged to a point at which no more current should 
be drawn, this voltage will fall to between 1.7 and 1.8 
for the cell. 

In making ordinary calculations it is customary 
to consider each cell as causing a pressure of two 



DYNAMO LIGHTING AND IGNITION 165 

volts so that a three-cell battery is called a six-volt 
battery. The current that a cell will give is meas- 
ured in ampere-hours or in watt-hours, generally by 
the former. An ampere-hour is the total quantity of 
current that passes in one hour if the flow is contin- 
uous at a rate of one ampere. An ampere-hour will 
also pass if a flow of one-half ampere is maintained 
for two hours. The number of ampere-hours is found 
by multiplying the number of amperes flowing by the 
time in hours. Batteries are generally rated accord- 
ing to their ampere-hour capacity, this capacity being 
based on discharging the battery in eight hours. A 
battery rated as a twenty ampere-hour battery would 
give a flow of one ampere for twenty hours or, theoret- 
ically, a flow of twenty amperes for one hour. This 
latter flow could not be secured in practice because of 
the action that would take place in the cells under 
such a heavy discharge rate. 

As previously stated, a charged cell has had its posi- 
tive plates changed to peroxide of lead and its nega- 
tives to sponge lead. When the battery is connected 
to the wiring circuits so that it lights the lamps, an 
action immediately begins to take place between the 
plates and the acid electrolyte. A part of the sulphuric 
acid in the liquid begins to combine with the lead in 
the plates to form lead sulphate and the plate material 
is gradually turned to this sulphate. The percentage 
of water in the electrolyte is increased because of the 
combining of part of the oxygen and the sulphur of 
the acid with the lead of the plates, leaving the hydro- 
gen and oxygen in the form of water, which is a 
combination of these two gases. The plates thus 
change slowly to lead sulphate, while the liquid 
becomes more nearly pure water. When the dis- 



166 THE MOTOR CYCLE HANDBOOK 

charge has continued until the normal output of the 
battery has been secured, it will be necessary to send 
a charging current through the cells in a direction 
the reverse of the flow that takes place during 
discharge. 

With the charging current flowing, the sulphate of 
the plates combines with part of the hydrogen and 
oxygen in the liquid to form sulphuric acid. The 
positive plate then becomes peroxide of lead and the 
negative is left as sponge lead. This transformation 
continues until the sulphate is completely reduced and 
the battery is then said to be charged. 

The greatest care that is necessary in allowing a 
battery to discharge is to see that it does not do so to 
such a point that the voltage becomes abnormally low. 
Under no conditions should discharge be continued 
when the voltage is 1.7 per cell, and if the current 
flow from the battery is carried past this point serious 
damage will result. 

From the explanation of the action during charge 
and discharge, it will be seen that the proportion of 
acid in the electrolyte will give an indication whether 
the battery is properly charged or nearly discharged. 
The acid is much heavier than water, and as the pro- 
portion of acid in the liquid becomes greater, the 
weight of the electrolyte becomes greater. Therefore, 
the heavier the electrolyte, the more nearly charged 
the battery is known to be. 

To find the condition cf the battery by testing the 
liquid, a hydrometer shown in Figure 80 is used. 
The hydrometer is a glass tube having a hollow bulb 
and a weight at one end and a thin tube with a num- 
bered scale at the other end. When this instrument 
is allowed to float in the liquid from the battery cells, 



DYNAMO LIGHTING AND IGNITION 



1G7 



the point on the scale to which it sinks indicates the 
weight of the liquid, because, of course, the hydrom- 
eter will not sink so deep into the heavy liquid with 
a large proportion of acid as it will into the liquid 



V 




Figure 80. — Left: Hydrometer Syringe. Right : Hydrometer 

Scale. 



when almost all water. The scale is graduated accord- 
ing to the weight of liquids, known as specific gravity, 
which is their weight compared to that of pure water. 
On the stem of the hydrometer appear numbers 
from 1.100 near the top, to 1.300 near the bottom. 



168 THE MOTOR CYCLE HANDBOOK 

"With the battery fully charged the hydrometer will 
sink only to the point between 1.250 and 1.300; but 
with a discharged battery whose electrolyte is mostly 
water the hydrometer will sink almost to the 1.100 
mark. Different degrees of charge are indicated by 
the hydrometer's sinking to points on the scale 
between the 1.100 and the 1.300 mark. The point 
indicated at the surface of the liquid is the specific 
gravity of the electrolyte. 

The hydrometer is carried in a tube with a nozzle 
at its lower end that may be inserted into the cells, 
and with a bulb at the upper end so that some of 
the electrolyte may be drawn from each of the cells 
for purposes of test. 

In the top of each cell of every battery will be 
seen a small plug. This plug may be unscrewed or 
released from its lock and will leave an opening ex- 
posed that passes into the interior of the cell and 
through which the electrolyte may be seen. The 
hydrometer syringe may be inserted into the cell, and 
when the bulb is squeezed and allowed to expand, 
some of the liquid will be drawn up into the tube 
and the hydrometer will float in this liquid. After 
all pressure has been released from the bulb the spe- 
cific gravity of that liquid may be noted on the 
hydrometer scale at the point where the instrument 
rises above the surface of the electrolyte. The gravity 
should then be noted and the liquid carefully returned 
to the same cell from which it was drawn. 

If this gravity is between 1.250 and 1.310, the cell 
is well charged. If the gravity is between 1.200 and 
1.250, the cell is at least half, but not fully, charged. 
Gravity between 1.150 and 1.200 indicates that the 
cell is nearly discharged while the gravity of 1.150 



JHTNAMO LIGHTING AND IGNITION 



169 



or below means that the cell is discharged to a point 
at which no further discharge should be allowed. 
If the battery is in good condition, the gravity will 




Figure 81. — Low Level of Liquid in a Battery. 

be within twenty-five points of the same in all cells. 
If there is a greater difference it usually indicates 
trouble in the cell or cells which are low. 



170 THE MOTOR CYCLE HANDBOOK 

Battery Care. — It is essential that the storage bat- 
tery have certain attention at regular intervals. The 
most important item in the care of a battery is that 
of adding pure water to each cell at least once each 
week during warm weather and at least every second 
week in cold weather. The water is added through 
the holes left with the vent plugs removed and may 
be easily handled by using the hydrometer syringe. 
A sufficient quantity of water should be placed in 
each cell to bring the surface of the liquid from one- 
quarter to three-eighths of an inch above the tops of 
the plates. The water used for this purpose must 
be distilled. Tap water or water that has been kept 
in metal containers must never be used. Except 
when some of the electrolyte has been spilled from one 
of the cells, nothing but pure water should ever be 
added. 

The specific gravity of each cell of the battery 
should be taken at regular intervals and if the whole 
battery is getting lower the fault should be looked 
for without delay. If one cell becomes lower, but the 
others remain normal, trouble in that cell is indicated. 
Care should be used when testing not to spill electro- 
lyte on top of the battery, as it will cause corrosion 
at the terminals and partial short-circuiting of the 
cells. If it is found that one cell always takes more 
water than others, it is probable that the jar for that 
cell has become broken. 

At the time of testing or adding water to the bat- 
tery, the terminals should be carefully examined for 
looseness or breakage, either at the connecting bars 
between the cells or at screwed or tapered connectors. 
No copper wires should ever be attached at the lead 
battery posts, as they will soon be eaten away by 



DYNAMO LIGHTING AND IGNITION 



171 



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172 THE MOTOR CYCLE HANDBOOK 

the action of the acid. Should the connections be 
found covered with corrosion or verdigris, they should 
be washed with ammonia water, and in any case 
should be covered with a coat of vaseline to prevent 
such action by the acid. 

The battery must be firmly secured so that move- 
ment from the motion of the cycle is impossible. If 
the battery case is wet or if the inside of the battery 
box is wet, the moisture should be wiped away with 
a cloth slightly moistened with ammonia water. 

THE DYNAMO 

The dynamo consists of a revolving armature operat- 
ing in connection with a stationary field. The rota- 
tion of the armature generates a flow of electric 
current in the armature, and the current passes out 
of the dynamo to the battery and other electrical 
parts. 

The most common form of armature is built by 
mounting on a shaft a sufficient number of soft iron 
disks to make a cylinder. This part is called the 
armature core. Running lengthwise of the core are 
a number of grooves or slots, these slots being of 
sufficient width and depth to allow a quantity of 
insulated wire to be wound on the core and in the 
slots The coils formed by this wire are called the 
armature windings, and it is in these windings that 
the current flow is first generated. One form of 
dynamo is shown in Figure 82. 

Various forms are adopted for the field magnet, 
the shape depending on the size and mounting that 
will be required for the particular machine being 
designed. The ends of the magnet are curved to bring 






DYNAMO LIGHTING AND IGNITION 



173 



them close to the armature and the cylindrical pass- 
age between them in which the armature rotates is 
called the armature tunnel. 

Should the magnets be formed with four or six 
ends, as is often the case, the ends are placed so that 
they form pairs on opposite sides of the armature 
and are directly across from each other as in 
Figure 83. 

The magnets that produce the field are made from 
soft iron, and the soft iron, called the magnet core, is 




Figure 83. — Flow of Field Magnetism in Four-Pole Dynamo. 



surrounded with a coil of insulated wire. When a 
flow of current passes through this wire, the soft iron 
becomes an electro-magnet. The coil of wire around 
the magnet core is called the field winding, and the 
current that passes through this winding to make the 
core magnetic is secured by taking a part of the cur- 
rent generated in the armature. 

As the armature rotates, the current caused to flow 
through the armature coil travels in one direction, 



174 THE MOTOR CYCLE HANDBOOK 

while the armature makes a half revolution, and then, 
on the next half revolution, the current is caused to 
pass in the opposite direction. Such current is not 
suitable for battery charging purposes, and in order 
to change this alternating current into a flow that 
always travels in one direction, the commutator is 
used. The current having a continuous direction of 
travel is called direct current, and is the only form 
suitable for battery charging. 

The commutator consists of a number of copper 
bars arranged in a circle around one end of the arma- 
ture shaft and fastened to the shaft so that they turn 
with it. These bars are insulated from each other. 
Each pair of copper bars is fastened to an arma- 
ture coil that rests in one pair of slots and the other 
bars are fastened to the other coils of wire that form 
the armature. 

Brushes, made from some material that carries 
electricity, are placed so that they rest against the 
surface of the commutator bars. The brushes are 
therefore in contact with the two ends of the arma- 
ture coil. Any flow of electric current generated in 
the armature winding will pass into these brushes. 

Now, bearing in mind the fact that the current 
reverses each half revolution, and also the fact that 
the commutator bar in contact with one brush at 
one position will have changed to the other brush 
when a half revolution has been made, it will be seen 
that the current will always be given to the brushes 
in the same direction as in Figure 84. 

From the brushes, wires and connections lead to 
the battery, lamps and other current-consuming de- 
vices, and in most cases to the field magnet windings 
also. The method of leading part of the generated 



DYNAMO LIGHTING AND IGNITION 



175 



current around the field magnets is one of the impor- 
tant considerations in dynamo design. 

With increase of dynamo speed, the pressure, meas- 
ured in volts, and the flow, measured in amperes, 
both increase in proportion. Unchecked increase in 
voltage and amperage would result in damage to the 
electrical parts. In order to prevent such damage 
various methods have been adopted for controlling the 
dynamo output. 

The voltage of the dynamo must be greater than 
the voltage of the battery in order that current may 
flow from dynamo to battery. Just as long as the 
dynamo voltage remains above that of the battery, 





Figure 84. — Action of Commutator in Maintaining 
Uni-Directional Flow From Armature. 



the flow will continue and the battery will receive a 
charge. When, however, the dynamo voltage falls 
below that of the battery, as it will when the dynamo 
is idle or running at very low speed, then the battery 
pressure or voltage will be greater than that of the 
dynamo, and if the two units remain connected 
through the wiring there will be a reverse flow from 
battery to dynamo. This reverse flow, if allowed to 
continue, will rapidly withdraw the current from the 
battery. To prevent such a useless and damaging 
battery discharge, the dynamo is disconnected from 
the battery when the dynamo voltage is too low to 
cause a flow of current to the battery. This is accom- 



176 THE MOTOR CYCLE HANDBOOK 

plisKed by an automatic switch acting to disconnect 
the dynamo and battery when the dynamo voltage 
falls below a certain limit and to establish the connec- 
tion again when the voltage rises to a point that 
allows of battery charging. This switch is called a 
reverse current cut-out, or simply a cut-out. 

The dynamo armature is driven from the engine 
so that its speed increases directly in proportion to 
increase of engine speed. The dynamo voltage would 
therefore naturally rise continuously from the lowest 
to the highest speeds. With the dynamo operating 
at a variable speed some method of output control 
is used to decrease the field strength with increase of 
speed so that the weakened field counteracts the more 
rapid rotation of the armature and the dynamo volt- 
age is held within certain desired limits. Most motor 
cycle dynamos are regulated by what is known as the 
third brush system in which there is gradual increase 
of voltage until a maximum is reached at some critical 
speed, followed by a falling off in voltage as the speed 
becomes still greater. 

Regulation, — The voltage between a brush of a 
two-pole dynamo and a point on the commutator away 
from this brush depends on the distance of the point 
from the brush and becomes greater as the distance 
increases. If one end of the shunt field winding be 
connected to one brush and the other end of the wind- 
ing lead to a brush that is not directly opposite the 
first one, the difference in voltage acting to send 
current through the shunt field will not be as great 
as if the field were connected between brushes directly 
opposite. The brush that carries one end of the wind- 
ing is generally made movable and the output of the 
dynamo may be increased or decreased by moving 



DYNAMO LIGHTING AND IGNITION 



177 



the brush away from or toward the stationary brush. 

At low speeds the flow of magnetic lines of force 
between the poles of the field magnet is practically 
straight across, and because of this direction of the 
lines of force through the armature, the coils which 
are at any instant in connection with the brushes 
cut through the greatest possible number of lines of 
force, and therefore the greatest difference in voltage 
will be between the commutator points being touched 
by the main brushes. 

With increase of armature speed, the lines of force 
do not continue to pass straight across but are car- 
ried part way around in the direction of rotation by 





Figure 85. — Distortion of Lines of Force Used in Third 
Brush Regulation. 

the core of the armature as shown in Figure 85. With 
the magnetism flowing in this distorted path, the arma- 
ture coils that are at any time attached to the 
regulating brush through the commutator are not cut- 
ting as many lines of force as at lower speeds, and* 
the voltage difference is less than with the lines of 
force passing straight across. This reduction of volt- 
age causes the amperage passing through the shunt 
field to decrease, and even with the rise in armature 
speed, the output does not increase proportionately 
because of the weakened field. With further increase 
of armature speed the path of the lines of force is 
still further distorted and the field current drops to 
such an amperage that the total output of the dynamo 



178 THE MOTOR CYCLE HANDBOOK 

becomes less and less through the highest speeds of 
rotation. 

DYNAMO CARE 

In order that the brushes may make a good contact 
the commutator surface must be smooth and perfectly 
cylindrical. Should the surface become dirty, 
scratched, rough or pitted it must be restored to good 
condition at once if the dynamo is to be maintained 
in good condition. Should an examination show it 
to be blackened or dirty it may be cleaned by hold- 
ing a soft cloth slightly moistened with gasoline 
against the commutator surface while the dynamo is 
being driven by the engine at the lowest possible 
speed. 

If the surface of the commutator is rough or slightly 
scratched and pitted it may be dressed smooth with 
sandpaper. Emery cloth or emery paper should never 
be used because emery is an electrical conductor and 
will short circuit the commutator bars. Before using 
the sandpaper the commutator should be cleaned as 
described and the holders and brushes should be so 
supported that they do not touch the commutator 
surface. The engine should be run at the lowest pos- 
sible speed so that the commutator is revolved. A 
strip of "000" sandpaper should then be cut just 
as wide as the commutator surface and this strip of 
paper should be placed over the end of a thin stick 
of equal width. By holding this paper against the 
surface of the revolving commutator slight scratches 
or pitting may be removed. 

After the surface is even and bright, the engine 
should be stopped and every trace of copper dust and 
sand should be removed from the interior of the 



DYNAMO LIGHTING AND IGNITION 179 

dynamo, either by wiping out with a cloth moistened 
with kerosene or by blowing out with air under 
pressure. 

The electrical resistance between brush and commu- 
tator depends on how well the brush end fits the com- 
mutator surface. For' this reason the brush ends 
should be properly fitted. This operation is per- 
formed as follows : 

A strip of "000" sandpaper should be cut so that 
it is at least as wide as, and preferably a little wider 
than, the end of the brush to be handled. With the 
dynamo idle, the brush should be drawn away from 
the surface of the commutator so that the strip of 




Figure 86. — Fitting- Brush End With Sandpaper. 

paper may be drawn between the brush end and the 
commutator with the sand side tow T ard the brush as 
in Figure 86. The paper should then be drawn back 
and forth under the brush end and should be held so 
that it follows the surface and curve of the commuta- 
tor while* passing under the brush. After all rough- 
ness and unevenness have been removed from the 
brush, the end should be carefully wiped with a clean 
soft cloth. All particles of dust should be removed 
from the interior of the dynamo with a cloth mois- 
tened with kerosene or by blowing them out with air. 
Each brush should be dressed in this way, even though 
only one seemed to need the treatment. Great care 



180 



THE MOTOR CYCLE HANDBOOK 



should be used in dressing the ends of the regulating 
brushes and they should always be dressed after mov- 
ing them to a new position. 

REMY EQUIPMENT 

Among the earlier models made by the Eemy Elec- 



/gn/f/on . 



Co/'/s 




Figure 87.^ — Wiring- Diagram of Remy Ignition Dynamo. 

trie Company, was an ignition dynamo of which a 
large number are still in use. A complete wiring dia- 
gram of this equipment is shown in Figure 87. Of 
the letters at the lighting switch, H indicates the head 
lamp wire; T the tail lamp; and S the dimmer lamp. 



DYNAMO LIGHTING AND IGNITION 181 

The dynamo contains a single field coil of the shunt 
wound type, two main brushes and one regulating 
brush. The outfit is of the six-volt type and the 
dynamo delivers a maximum current of four and a 
half amperes. 

The cut-out is of a peculiar type, being operated by 
vacuum from the engine inlet. The construction is 
shown in Figure 88. The vacuum created in the 
inlet pipe when the engine is started acts upon the 
cut-out and draws the contacts together. This makes 
a connection between the battery and dynamo which 
is maintained until the engine stops running. 




Figure 88. — Construction of Remy Vacuum Cut-Out. 

The ignition unit is carried underneath the dynamo 
as shown in the wiring diagram. The two ignition 
coils are carried on top of the electrical unit. Details 
of the ignition breaker are shown in the Figure 89. 
The breaker consists of a pair of contacts whose opera- 
tion determines the time of sparking and within the 
same mechanism is carried a set of metal contacts 
made up of upper and lower members between which 
moves an arm carrying a central contact. This serves 
to send ignition current to either one or the other 
of the two coils, depending on which cylinder is to 
be fired. The appearance of the cut-out and lighting 
switch is shown in Figure 90. 



182 THE MOTOR CYCLE HANDBOOK 

A later model of Eemy equipment includes a shunt 
wound dynamo having two field coils, two main 
brushes and one regulating brush. A complete wiring 
diagram is shown in Figure 91. This equipment is 




Figure 89. — Ignition Breaker Used With Remy Ignition 

of the six-volt type and gives a maximum output of 
four amperes. 

The cut-out is of the centrifugal type and its appear- 
ance on the end of the dynamo is shown in Figure 92. 
In the illustration, 1 indicates a fastening for the 
regulating brush and 2 indicates the brush itself. 



DYNAMO LIGHTING AND IGNITION 



183 



A type of battery ignition mechanism for motor 
cycles that is very similar to the generally used auto- 
mobile type of equipment is shown in Figure 93. This 
unit includes a breaker whose contacts are shown at 
9 and which is operated by the cam 8 striking the 




Figure 90. — Position of Cut-Out and Lighting: Switch on 
Remy Ignition Dynamo. 



bumper 7. The contacts are provided with an adjust- 
ment at 10 which is locked by the jam nut 11. Above 
the breaker is carried the distributor whose rotating 
member 5 is fitted with a spring contact 4 which bears 



184 



THE MOTOR CYCLE HANDBOOK 




DYNAMO LIGHTING AND IGNITION 



185 



against contact 14 and carries high tension current 
through wire 15 from the ignition coil 16. With the 
device in action, high tension current from rotor 5 
passes to the segments 2 from which wires lead to the 




Figure 92. — Commutator End of Remy Dynamo Showing 1 

Centrifugal Cut-Out Contacts at the Right. The 

Regulating- Brush Screw Is Shown at 1 

and the Regulating Brush at 2. 



spark plugs. Primary current between the breaker 
and the coil is carried throught wire 12. The distrib- 
utor cap 3 is held in proper position by the lug 1, 
engaging the recess 6 while the spring 13 serves to 
lock the entire assembly. 



186 



THE MOTOR CYCLE HANDBOOK 




Figure 93, — Remy Battery Ignition System. 



DYNAMO LIGHTING AND IGNITION 



187 



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188 THE MOTOR CYCLE HANDBOOK 

SPLITDORF EQUIPMENT 

One of the first units made by the Splitdorf Elec- 
trical Company was known as the Mag-dynamo. This 
outfit consisted of a high tension magneto above which 
was carried a shunt wound dynamo having two field 
coils and two brushes. The equipment was of the 
six-volt type with a maximum output of three amperes. 

This Mag-dynamo includes a centrifugally operated 
controlling device having two sets of contacts as shown 




Figure 95. — Appearance of Centrifugal Cut-Out on Splitdorf 

Dynamo. 

in the wiring diagram Figure 94. With the driving 
shaft in motion, the controller weights force the cen- 
tral plunger in the direction indicated by the arrow. 
This movement causes the left-hand pair of contacts 
to close and these serve as a cut-out, connecting the 
dynamo with the battery. With an increase of dynamo 
speed the central pair of contacts is closed and this 
action reduces the field strength and thus controls 
the output. A starting button is provided whose clos- 
ing causes the dynamo to act as a motor and, by ener- 



DYNAMO LIGHTING AND IGNITION 



189 




Figure SQ. — Construction of Splitdorf Dynamo Having 
Centrifugal Cut-Out. 




Figure 97. — End Views of Splitdorf Motor Cycle Dynamo. 



190 THE MOTOR CYCLE HANDBOOK 

gizing the fields with storage battery current, a hot 
spark is produced for starting. 

A later type of separate dynamo made by the Split- 
dorf Electrical Company is shown in Figure 95. This 
unit is of the shunt wound type having two field coils, 
two main brushes and one regulating brush. It is of 




Figure 98. — Centrifugal Cut-Out on Splitdorf Dynamo. 

the six-volt type and gives a maximum current of 
four and a half amperes. Details of the construction 
are shown in Figures 96 and 97. 

The cut-out, shown in Figure 98, is of the centrifu- 
gal type operated by a ring weight type of governor 
carried on the commutator end of the dynamo. The 
complete wiring connections are shown in Figure 99. 



DYNAMO LIGHTING AND IGNITION 



191 




CHAPTER VII 
DRIVING PARTS 

The driving or transmission system of the motor 
cycle includes a clutch which allows the engine either 
to run free from the road wheel or to be connected 
with that wheel, also a gear-set or transmission proper 
which provides for various ratios of speed between 
the engine and the road wheel. The clutch and trans- 
mission are, as a rule, combined into one unit. 

Between the transmission and the rear wheel, power 
is carried by chains, gears, shafts, or belts, or else by 
some combination of these methods. Two parts which 
would properly be classed as controls are, for conven- 
ience, included in the transmission system, these two 
being the kick starter and the brakes. 

The Clutch, — Motor cycle clutches consist of two 
sets of disks or plates, one set being attached to the 
engine and the other to the drive. For operating the 
motor cycle these two sets of disks are held in contact 
with each other by one or more springs as shown in 
Figure 100. 

The clutch may be located outside of the trans- 
mission as shown in Figure 101 and in such a con- 
struction the plates are oftentimes designed to operate 
dry and without any lubrication between their con- 
tact surfaces. In other cases, as shown in Figue 102, 
the clutch is carried inside of the transmission housing 
and it then operates in the same bath of oil that serves 

192 



DRIVING PARTS 



193 



to lubricate the transmission. The clutch may also 
be a separate unit from the transmission but may still 
be lubricated, sometimes being enclosed with the driv- 
ing gears as shown in Figure 103. 

When the clutch springs are allowed to expand and 
press the disks together, the clutch is said to be 




Figure 100. — Three Plate Clutch Carried in Sprocket 
(Triumph). 

engaged and the power of the engine is carried 
through it to the transmission or to the driving parts. 
When the clutch springs are compressed, their ten- 
sion is removed from the disks, the disks are allowed 
to separate and the engine allowed to run free from 



194 



THE MOTOR CYCLE HANDBOOK 






the driving parts. The clutch is then said to be dis- 
engaged and this disengagement is accomplished either 
by means of a foot pedal, by a hand lever or by a com- 
bination of pedal and lever. 

The clutch control allows the rider to keep the 
engine running with the motor cycle standing still and 
then, by slowly engaging the clutch, to pick up the 




Figure 101. — Clutch Carried in Housing Outside of Gear-Set 
(Excelsior). 



load and start the machine in motion. The clutch may 
be used as a cushion for the power impulses by holding 
it slightly disengaged so that the partial slipping 
allows a smooth drive. If the clutch is properly 
adjusted this slipping will be provided for and the 
same adjustment will often allow the rider to increase 
the pressure on the disks in case of an exceedingly 



DRIVING PARTS 



195 



hard pull. The detailed construction of a typical 
multiple disk clutch is shown in Figure 104. In this 
particular example the spring pressure is controlled 
by turning the screw shown at the extreme left in 
the center. 

In some designs the clutch is actuated by a series 
of small coiled springs as shown in Figure 105, while 




Figure 102. — Clutch Carried Inside of Gear-Set Housing 
(B. S. A.). 



in other cases pressure is applied by one comparatively 
large spring as shown toward the left in Figue 106. 
Clutch Adjustment. — If a clutch does not release 
or does not engage properly the- trouble is more often 
due to faults in the control connections than to an 
incorrect tension of the clutch springs. It is neces- 
sary, with the clutch in the fully engaged position, 
that there still remain some free movement of the 
operating pedal or lever for otherwise a part of the 



196 



THE MOTOR CYCLE HANDBOOK 




Figure 103. — Clutch Carried Inside of Worm Gear (Cleve- 
land). 



DRIVING PARTS 



197 



spring pressure will be carried by the operating parts 
and this lost pressure will not be available for holding 
the disks together. A typical arrangement of connec- 
tions between clutch and transmission parts and the 
control pedal and lever is shown in Figue 107. 

If it has been found that the controls have the nee- 




Figure 104.- 



-Construction of Multiple Disc Clutch with Re- 
lease Screw (Excelsior). 



essary free movement when the clutch is fully engaged 
and if the disks still fail to hold, it may be necessary 
to adjust the tension of the springs. However, this 
adjustment should not be made until it has been made 
sure that the disks are clean and in good condition. 
Using the Clutch. — ^vVith the usual form of clutch 



198 



THE MOTOR CYCLE HANDBOOK 



control in which this member is operated both by a foot 
pedal and by a hand lever, the clutch will engage 
only to an extent determined by the position of the 
hand lever, this being true even though the foot pedal 
be entirely released. The position of the hand lever 




Figure 105. — Multiple Disc Clutch on End of Transmission 
Housing" (Indian). 



determines the amount of clutch spring tension that 
can act upon the disks, and the use of the foot pedal 
will have no effect on the amount of this tension. The 
foot pedal is used during the operations of starting, 
stopping and slowing-up. Because the two controls 



DRIVING PARTS 199 

are adapted for different uses it is best that the rider 
should become thoroughly familiar with the use of 
both lever and pedal. 

A smooth drive can be obtained by setting the clutch 
lever in such a position that the disks are allowed to 
absorb the shocks which result from the power 
impulses of the engine. Such use of the clutch will 
render it comparatively easy to drive slowly through 
traffic. It might be mentioned that choking of the 
engine will be avoided while the motor cycle is run- 
ning at a low rate of speed for some distance if the 
clutch is frequently released and the engine is speeded 
up for a few seconds while it is released. 

According to the practice followed in driving an 
automobile, the engine speed is decreased by closing 
the throttle as soon as the clutch is disengaged and 
is allowed to remain thus while the transmission gears 
are being shifted. Theoretically this would also apply 
to the motor cycle, but in actual practice it will usu- 
ally be found that the gears are changed so quickly 
after disengaging the clutch that closing of the throt- 
tle will be unnecessary for the engine has no time 
in which to race. 

Clutch Troubles. — Incorrect operation of the clutch 
may be in either of two ways, dragging or slipping. 
Either of these troubles may be due to a wrong adjust- 
ment of the operating connections or to a wrong 
adjustment of the spring tension. A dragging clutch 
may also be caused by disks that are improperly fitted 
or that have become warped. A slipping clutch will 
result if the disks are badly worn or if disks that are 
designed to operate dry become covered with oil or 
grease. 

If the plates of a dry disk clutch are found to be 



200 



THE MOTOR CYCLE HANDBOOK 




Figure 106. — Clutch Actuated by Single Coiled Spring (Har- 
ley-Davidson). 



DRIVING PARTS 



201 



greasy or glazed, it will be necessary to remove them 
and to clean the surfaces with gasoline. The surface 
of the disks can be slightly roughened with a wire 
brush. It is a somewhat common practice to burn 
the oil out of clutch facings with a blow torch. While 




Figure 107. — Lever and Pedal Controls for Clutch and Gear 
Set (B. S. A.). 



this method is effective in removing oil there is some 
danger of warping the metal plates on which the fric- 
tion surfaces are mounted. 

When adjusting the tension of a clutch having 



202 THE MOTOR CYCLE HANDBOOK 

several springs, care should be used to turn each 
adjusting bolt or nut exactly the same number of 
turns or parts of a turn regardless of how hard some 
of them may turn and how easy it may be to move 
the others. After a clutch is adjusted it may be 
tested by placing the machine on the stand, and with 
the clutch engaged, attempting to turn the rear wheel. 
Should it be found that the clutch tends to grab in 
spite of careful adjustment it may be necessary to 
place a few drops of oil on the friction surfaces. 

If new disks are fitted in a clutch it is important 
that their slots or openings fit the clutch keys prop- 
erly. A proper fitting means that there is practically 
no side play, while the disk is still free to move end- 
wise along the key, especially along that portion of 
the key which carries the disk while in working posi- 
tion. If the disks are loose on the keys the clutch 
will be noisy. In taking a clutch apart it is a good 
plan to mark each of the plates, both as to their posi- 
tion with reference to each other and for their position 
on the keys. 

THE GEAR-SET 

A majority of motor cycles are fitted with a series 
of gears which allow three different ratios of speed 
between the engine and drive wheel. A few machines 
provide only two forward speeds while still others 
have three forward speeds and also a reverse gear. 
Because of the general use of the three speed gear 
it will be described in detail. 

A typical three speed gear box is shown in Figure 
108. Within the housing are carried two shafts, the 
upper one being called the main shaft and the lower 
one C being called the counter-shaft. The main shaft 






DRIVING PARTS 



203 



has its right hand end carried by a ball bearing in the 
housing, while its left hand end passes through the 
center of a gear and a sprocket and extends out to 
the taper shown at the extreme left. On the main 
shaft is mounted a sliding member consisting of the 
gears 2 and 4 together with the jaws B, these three 




Figure 108. — Parts of Three Speed Gear-Set. A, B: High 
Speed Jaws. 1 : Constant Mesh Sprocket Gear. 2 : In- 
termediate Speed Main Shaft Gear. 3 : Intermediate 
Speed Countershaft Gear. 4 : Low Speed Main 
Shaft Gear. 5 : Low Speed Countershaft 
Gear. 6 : Constant Mesh Countershaft 
Gear (Indian). 

parts being made in one piece and adapted to slide 
along splines formed on the outside of the main shaft. 
The counter-shaft carries three gears, 3, 5 and 6, 
formed in one piece with the shaft. Power from the 
engine comes to the gear-set through the clutch 
to the tapered end of the main shaft. With the engine 



204 THE MOTOR CYCLE HANDBOOK 

running and the clutch engaged, the main shafts 
together with gears 2 and 4 are put in motion but as 
neither 2 nor 4 are in mesh with the counter-shaft 
gears, no power is transmitted through the gear-set. 

When it is desired to engage low speed in which the 
engine runs fast compared to the road wheel, the slid- 
ing member on the main shaft is moved to the right 
until gear 4 engages gear 5. Power now passes 
through the main shaft and gears 4 and 5 to the 
counter-shaft. As gear 4 is smaller than gear 5 the 
counter-shaft runs at less speed than the main shaft. 
Gear 6 on the counter-shaft is always in mesh with 
gear 1 and gear 1 is attached to the spocket which is 
shown in section at the left hand side of the illustra- 
tion. Over this spocket passes the drive chain which 
carries power to the rear wheel. Inasmuch as gear 6 
is smaller than gear 1, gear 1 and the drive sprocket 
run at a lower speed than that of the counter-shaft 
so that the total reduction of speed between the main 
shaft and the drive sprocket is considerable. 

When the intermediate gear ratio is to be used the 
sliding member of the main shaft is moved to the 
left until gear 4 leaves its engagement with gear 5 
and until gear 2 meshes with gear 3 on the counter- 
shaft. As the gears 2 and 3 are of the same size, 
the counter-shaft now runs at the same speed as the 
main shaft and the only reduction remaining is due 
to the difference in size between gears 6 and 1. 

When high speed or direct drive is to be used the 
sliding member on the main shaft is moved still far- 
ther to the left until gear 2 passes out of engagement 
with gear 3 and until jaws A and B lock together. 
The drive sprocket and the main shaft now run at 
the same speed. 



DRIVING PARTS 



205 



A construction in which the sliding member consists 
of one gear and two sets of jaws is shown in Figure 
109. With this design there are two sets of constant 
mesh gears, these being shown at the extreme ends of 
the two shafts. With the sliding member moved to 
the right the low speed jaws are engaged and the 




Figure 109. — Gear Set Having- Two Pairs of Constant Mesh 

Gears and Two Pairs of Jaw Clutches 

(Reading Standard). 



sliding member locks the adjacent small gear to the 
main shaft through the jaws. Otherwise the action is 
similar to the gear-set already described. In Figure 
108 the connection for the kick starter is shown at 
the right hand end of the main shaft. Another trans- 
mission using jaw clutches is shown in Figure 110. 



206 



THE MOTOR CYCLE HANDBOOK 



Various gear ratios are used, the reduction depend- 
ing upon the weight of the motor cycle and the power 
of its engine. The average in direct drive is four and 
a half to one, but the range is from three and three- 
quarters to one up to six to one. The average reduc- 
tion in intermediate is a little greater than seven to 
one, w^hile the average reduction in low speed is about 
ten and one-half to one. When the reverse is used 




Figure 110. — Gear Set With Two Pairs of Jaw Clutches 

(B. S. A.). 



its reduction is usually somewhat greater than low 
speed, often being about twelve to one. 

It will be noticed that in the gear-sets so far 
described, it is necessary to pass through intermediate 
speed when going from low to high. This type of 
construction is known as a progressive sliding gear 
transmission. Another type is generally used when a 
reverse gear is supplied. In this other type, called 
a selective sliding gear, the sliding member on the 
main shaft is made in two separate parts, one part 



DRIVING PARTo 



>07 



being moved to engage low speed and reverse while 
the other part is moved to engage intermediate and 
high. With such a construction either of the sliding 
members may be moved independently of the other 
so that it is possible to pass from any one ratio 




Figure 111. — Heel and Toe Pedal for Operating- Two Speed 
Transmission. 

directly to any other ratio without going through any 
of the speeds that are not to be used. 

As a general rule, the transmission and clutch form 
a unit separate from the engine and mounted on the 
frame just back of the engine. In other designs the 
transmission may be built in a unit with the engine, 
this often being the case with four-cylinder machines. 



208 



1VCE MCTCR CYCLE HANDBOOK 



With some machines, especially with those providing 
only two speeds, the transmission gears are controlled 
by a double foot pedal as shown in Figure 111. Pres- 




Figure 112.- 



-Positions of Gear Shift Lever for Three Speed 
Transmission (Indian). 



sure on the forward pedal engages one of the ratios 
while pressure on the rear pedal moves the lever in 
the opposite direction and engages the other ratio. 



DRIVING PARTS 



209> 




210 



THE MOTOR CYCLE HANDBOOK 



The several positions for the control lever of a 
three speed progressive transmission are shown in 
Figure 112. 

Some machines are provided with a device called a 
free engine clutch shown in Figure 113. This simply 
consists of a jaw clutch which may be moved into 
or out of engagement. When it is engaged, the engine 
drive is carried through the tapered shaft to one 
clutch member and through the clutch to the driving 
sprocket. Such a device provides a suitable location 
for the kick starter. 




TMg-ure 114. — Free Engine Clutch Mounted in Wheel Hub 

(B. S. A.). 



A type of free engine device mounted in the wheel 
hub is shown by Figure 114. The clutch proper con- 
sists of three members, a steel central clutch piece 
having conical faces, and two phosphor bronze end 
clutch pieces which are tapered internally and adapted 
to engage with the steel central clutch piece 

The central clutch piece is engaged with the driving 
center to which is attached the belt pulley and the 
two phosphor bronze end clutch pieces are fixed in 
the hub shell. On the end of the driving center oppo- 
site the belt pulley is attached the free wheel mech- 



DRIVING PARTS 



211 



anism, and the pawl carrier also forms an abutment 
plate for the clutch pieces. 

On the belt pulley end of the driving center, there 
is a fixed spring plate which takes the pressure of 
the springs, and in between the springs and the phos- 




Figure 115. — Two Speed Planetary Transmission (Iver- 
Johnson). 

phor bronze end clutch piece is another plate which 
is actuated by means of the rod in the center of the 
spindle either to free the clutch, or to allow the 
springs to exert their pressure on the clutch pieces. 
By reason of the wedging action of the phosphor 
bronze pieces being forced onto the steel central clutch 



212 



THE MOTOR CYCLE HANDBOOK 



piece, the driving center is enabled to drive the hub 
shell. It will be seen that when the clutch is in action 
the spring thrust is self-contained and exerts no pres- 
sure on the ball races. 

In Figure 115 is shown a planetary type of two 
speed transmission. This arrangement consists of a 




Figure 116. — Planetary Transmission Showing- High Speed 
Clutch and Belt Pulley (Bradbury). 



central gear driven from the engine crankshaft. In 
mesh with this central gear are two or more small 
planetary pinions and these pinions are arranged to 
travel inside of a large internally toothed gear. The 
pinions are mounted on a plate which is in turn 
attached to the drive sprocket. When it is desired to 



DRIVING PARTS 213 

obtain a reduction of speed the internally toothed gear 
is held stationary by means of the band which is 
shown. With the central gear being driven by the 
engine, it causes the planetary pinions to travel around 
the inside of the internal gear but they travel at a 
rate of speed that is much less than the engine speed. 
High gear is secured by locking all of the gears 
together through a clutch so that they revolve as a 
unit and at the same speed as the engine. Another 
planetary gear operating upon the same principle 
but showing some difference in construction, is shown 
in Figure 116. 

Transmission Operation and Care. — With the slid- 
ing gear type of transmission, the shift from one ratio 
to another should only be made while the clutch is 
held released. When attempting to engage low gear, 
if it is found that the control level does not easily 
move into position it is due to the fact that the gear 
teeth or the jaws are meeting end-on. The trouble 
may be overcome by moving the motor cycle backward 
or forward. 

After low gear is engaged and the machine has been 
started in motion, the change to intermediate speed 
should be made without delay. The control lever 
should be moved quickly but should not be moved with 
a jerk. It is not safe to attempt to shift gears while 
running at speeds in excess of fifteen miles an hour 
because such practice will probably result in mechan- 
ical damage. 

If the engine has been stopped with the gears in 
the high speed or intermediate speed position, it will 
be found difficult if not impossible to move the con- 
trol into the low speed position. The shift may be 
made under these conditions if the lever is pulled 



214 



THE MOTOR CYCLE HANDBOOK 



while the engine is cranked by means of the starter. 
In shifting downward from high speed to interme- 
diate or from intermediate to low, it will be found to 
facilitate matters if the engine is slightly speeded up 
while making the change, this being just the reverse 
of the shift to higher gears in which the engine speed 




Figure 117. — Mounting of Kick Starter Pedal (Harley- 
Davidson). 

should be reduced. When shifting down it will be 
found best to release the clutch but slightly while 
making the change. 

The gear-set does a great deal of work and requires 
proper and ample lubrication. The gear box should 
have a supply of heavy oil such as steam engine cyl- 



DRIVING PARTS 



215 



inder oil or extra heavy gasoline engine oil. No kind 
of grease should be used in a transmission having ball 
or roller bearings. Gear boxes are designed to be 
filled from one-third to two-thirds full of lubricant 
but they should never be completely filled. 




Figure 118. — Kick Starter Connection with Gear-Set 
(Harley-Davidson). 



KICK STARTERS 



Motor cycle engines are generally cranked by means 
of a foot operated device attached to the gear-set and 
known as the kick starter. In a majority of cases 
the starter acts on the counter-shaft through a ratchet 
or an auxiliary sliding gear or some other means of 
engagement. The external appearance of one such 
starter is shown in Figure 117. By pushing down 
on the foot pedal the transmission shafts are rotated 



1>1G 



THE MOTOR CYCLE HANDBOOK 



and through the driving connection the engine crank- 
shaft is revolved. The relation of the starter to the 
gear-set is shown in Figure 118. In the particular 
installation just mentioned, connection between the 
pedal and the transmission shaft is secured through 
a gear on the shaft and a segment of a gear attached 
to the pedal as shown in Figure 119. This device is 
fitted with an adjusting plunger S. If the teeth of 




Pig-ure 119. — Kick Starter Gear Meshing- Device (Harley- 
Davidson). 



the segment fail to engage with the teeth of the gear 
because teeth 1 and teeth 2 do not align, stepping on 
the plunger will bring the gears into mesh. 

The arrangement of parts in another form of kick 
starter is shown in Figure 120. In this case the seg- 
ment engages with a gear carried outside of the 
ratchet and connecting with one of the transmission 
shafts. An arrangement by means of which the starter 
operates through an auxiliary shaft and gear extend- 
ing into the transmission is shown in Figure 121. The 



DRIVING PARTS 



217 



connection of the starter pedal on the unit power 
plant with a four-cylinder engine is shown in Fig- 
ure 122. 

Using the Starter. — When the engine is to be 
cranked by means of the kick starter, the spark and 




Figure 120. — Kick Starter Segment and Gear (Excelsior). 

throttle controls are set in their correct position for 
this purpose, the compression release is raised and 
the clutch allowed to remain engaged. Depending on 
the construction of the starter, the transmission gears 
are placed either in the neutral, the low speed or the 
high speed position. 



218 THE MOTOR CYCLE HANDBOOK 

The starter pedal is brought into its operating posi- 
tion and pushed downward until the engine compres- 
sion is felt. The starter pedal should then be allowed 
to return to the beginning of its stroke. The pedal 
is then pushed down quickly and when it is about half 
way through the stroke, the compression release is 
dropped. The engine should then start to fire but 
if it does not do so the starter is again used in the 
same manner. After the pedal has been pushed all 
the way down it should not be allowed to fly back 
under the action of its return spring because this 
will quite likely result in breakage. The operator's 
foot should be kept on the pedal until the parts have 
returned to their inoperative position. 

CHAIN DRIVE 

Cleaning and Lubrication. — The drive chains should 
be cleaned and lubricated at least once in each one 
thousand miles running because a dirty or poorly lub- 
ricated chain will give a jerky drive, will break easily 
and will tend to ride the sprockets. In many cases 
the short front driving chain is lubricated by oil vapor 
coming from the engine but this lubrication alone is 
not sufficient and both front and rear chains should 
be treated alike. The application of lubrication only 
to the outside links which are exposed is not the proper 
way to do this work. 

The chains should be removed and placed in a bath 
of kerosene or gasoline. In this bath the chain can 
be washed about until all grit and dirt is carried away. 
The chain should then be allowed to dry. Lubrication 
is applied by melting a specially prepared compound 
or else by making a mixture of tallow and graphite 






DRIVING PARTS 



210 



which is also used while melted. The chain should be 
placed in this lubricant and allowed to remain while 
heat is applied for ten or fifteen minutes so that the 
grease is able to reach underneath the rollers. The 
chain should be moved about while in the lubricating 




Figure 121. — Kick Starter Carried Into Gear-Set Housing 

(B. S. A.). 



bath. After the chain is removed and allowed to cool, 
the excess grease is wiped away with a clean cloth 
after which the chain is ready for use. Chains that 
run enclosed do not require attention as often as 
those which are exposed. The enclosed chains are 



220 



THE MOTOR CYCLE HANDBOOK 



generally run with a quantity of thick oil in the bot- 
tom of the case. 

Chain Adjustment. — If a drive chain is run too 
tight it will break, while if it is run too loose it will 
jump the sprockets. Motor cycle chains are adjusted 
somewhat tighter than are those on bicycles because 
of the steadier drive with the motor cycle. Both the 
long and the short chains should be adjusted so that 
they have a sag of about one-half inch on the lower 




Figure 122.- 



-Kick Starter Mounted on Unit Power Plant 
(Henderson). 



side. This sag should be tested at various points while 
turning the rear wheel until a full revolution has been 
made. The adjustment should be made while at the 
tightest point. In most designs the tension of both 
front and rear chains is dependent on the position of 
the gear-set. Therefore, if the front chain is adjusted 



DRIVING PARTS 221 

it will usually mean that the rear one also must be 
cared for. When both chains are to be attended to, 
the front one should be adjusted first. 

The driving chain between the engine and trans- 
mission is usually adjusted by loosening the fastening 
of the gear-set and moving the box into the correct 
position where it is firmly locked. After a front chain 
adjustment it will often be found necessary to change 
the length of the clutch and gear-shift controls. The 
rear drive chain is adjusted by loosening the fasten- 
ings of the wheel hub and moving the hub backward 
until the desired tension is secured. This movement 
may often be made with adjusting screws, one on each 
end of the hub. Care should be used to turn each 
screw exactly the same amount. After the chains 
have been adjusted the motor cycle should be placed 
on its stand and the rear wheel turned slowly while 
checking the tension in several positions. If the ten- 
sion is found correct the engine should be started and 
the various controls should be operated to see that 
they are correctly set. 

Chain Alignment. — Two sprockets over which a 
drive chain is running must be exactly in line with 
each other. If the sockets are in line the chain will 
not touch the sides of the teeth, while if they are out 
of line there will be interference and damage due to 
the wear on both chain and sprocket. If an examina- 
tion of a chain shows signs of wear on the inside of 
the side plates of the links it indicates a misalignment. 

The sprocket position cannot be correctly deter- 
mined by sighting. The correct method is to hold 
a straight-edge solidly across the face of one sprocket, 
preferably the larger one, and to allow the other end 
of the straight-edge to rest in the space between two 



222 THE MOTOR CYCLE HANDBOOK 

teeth of the other sprocket. If the sprockets are in 
line the end of the straight-edge will come flush with 
the bottom face of the teeth (not at the top of the 
teeth). 

Chain Renewal. — While a chain is removed for 
cleaning and lubricating, each link should be inspected. 
If any of them show a great amount of play between 
the pins and rollers, if they show broken rollers or if 
they contain loose pins, the defective links should be 
removed and replaced with new ones. The sprockets 
should also be examined for excessive wear on the driv- 




Figure 123. — Layout of Double Chain Drive. A: Engine 

Driving- Sprocket. B : Front Driven Sprocket. C : Front 

Driving Sprocket. D: Rear Driven Sprocket. 

ing or front side of the teeth. The teeth will wear 
hook-shaped in time and this will prevent proper 
meshing of the chain. The small sprockets will show 
more wear than the large ones. If a new chain is put 
on badly worn sprockets, it will make an unsatisfac- 
tory drive and the new chain will soon be ruined. 

Gear Ratios. — Chain drives are usually laid out 
somewhat as shown in Figure 123. Sprocket A is the 
engine sprocket; B is the front driven sprocket; C 
is the front driving sprocket ; while D is the rear wheel 
sprocket. To find the gear ratio, the number of teeth 
on the rear wheel spocket D is multiplied by the num- 



DRIVING PARTS 223 

ber of teeth on the front driven sprocket B. This 
product is divided by a number found by multiplying 1 
the number of teeth on the engine sprocket A by the 
number of teeth on the front driving sprocket C, the 
quotient being the total gear ratio. Using the letters 
shown in the diagram, this method may be explained 
by the following formula: 

DXB-^AXC 

BELT DRIVE 

Driving belts shouM be kept clean and free from 
collections cf grease, dirt and engine oil. They should 
occasionally be wiped with a moist cloth. No mineral 
lubricating oil such as engine oil should ever be 
applied to a belt and neither should any vegetable oil 
such as castor oil be used. In order to keep the belt 
soft and pliable it may be given a light application of 
neatsfoot oil once during each two or three weeks' 
driving. It may occasionally be necessary to clean 
the sides of a V belt with a file in order to remove 
dirt and roughness. Belt fastenings should be oiled 
and kept free from rust. 

Belt Adjustment. — Belt tension should be such that 
there is little or no slipping under any conditions of 
driving but it should not be so tight as to strain the 
bearings of the pulleys at either end. With a correct 
tension the belt will not slip when the motor cycle is 
pushed forward against the compression of the engine. 
The lower the gear ratio, that is, the faster the engine 
runs for a given road speed, the tighter the belt must 
be. A tight belt will wear faster than a loose one, 
although excessive looseness will cause wear because 



224 THE MOTOR CYCCE HANDBOOK 

of the slipping that takes place. A belt may be made 
tighter by cutting off a short piece from one end and 
then replacing the fastener, or else by the use of an 
adjustable pulley. 

Should it be necessary to remove the belt it will be 
best handled by removing it from the large pulley 
first and by replacing it over the small pulley first. 
When the belt is to be removed start it over the rim 
of the large pulley. When it is to be replaced put 
the belt over the engine pulley, then over the top of 




Figure 124. — Lapping- the Splices in a V or Flat Belt Drive. 

the large pulley, and turn the road wheel backward 
to finish the replacement. 

A spliced belt should be put over the pulleys in 
such a direction that the splice will be rolled down 
as it runs over the idler pulley if one is used. Should 
the splice start to curl up, the loose ends should be 
trimmed off and the direction of the belt's running 
should be looked after. The proper position for the 
splice is shown in Figure 124. 

Belt Pulleys. — Some machines having a belt drive 
are equipped with an adjustable pulley which allows 
of belt tightening or of a ready change of gear ratio. 



DRIVING PARTS 225 

Such pulleys are made for use with V belts and the 
outer flange of the pulley is made so that by turning 
it one way or the other the distance between the flanges 
will be increased or decreased. With the distance 
increased, the belt will lie lower in the pulley and the 
gear ratio will be lowei\ AVith the distance decreased 
the belt will ride higher and the gear ratio will be 




Figure 125. — Cushion Drive (B. S. A.). 

higher. Such adjustment will call for change in the 
length of the belt. This is sometimes cared fcr by 
having a comparatively short length at some one point 
in the belt and then carrying other lengths already 
fitted with the necessary parts of belt fastenings. 

OTHER DRIVES 

Many chain drives are fitted with cushion sprockets 
similar to the one shown in Figure 125. In this case 
the engine drives the central member which is shown 



226 



THE MOTOR CYCLE HANDBOOK 



in white. The sprocket teeth or the pulley flanges 
are attached to the part shown shaded. Between the 
driving and driven members is a series of coiled 
springs, which by their compression and expansion 




Figure 126. — Cushion Drive Sprocket (Excelsior). 

absorb any small shocks due to the power impulses 
of the engine. Another cushion drive sprocket is 
shown in Figure 126. 

A worm gear drive for motor cycles is shown in 
Figure 127. This consists of a steel worm attached 
to and driven from the transmission shaft. This worm 
drives a worm gear which is made of bronze and this 



DRIVING PARTS 227 

worm gear in turn drives through the clutch and chain 
to the rear wheel. 

BRAKES 

Motor cycle brakes were originally the same as, or 
very similar to, the coaster brake used with bicycles. 




Figure 127. — Worm Gear Drive (Cleveland). 

A motor cycle type is shown in Figure 128. In the 
larger and more powerful machine these coaster brakes 
have given way to brakes designed very much along 
the lines of those used with automobiles, that is, 
brakes of the drum type with an expanding shoe inside 
the drum or with a contracting band outside the drum. 
In many cases the brake is made with both an internal 
shoe and an external band. Brakes are usually con- 



228 



THE MOTOR CYCLE HANDBOOK 



trolled from a foot pedal although in a few cases a 
hand grip is used. In American practice the brake 
is located on the hub of the rear wheel. In foreign 
machines brakes are also found applied to the belt 
pulley on the rear wheel as shown in Figures 129 
and 130, and to a special brake pulley fastened to 
the front wheel as shown in Figure 121. 
j The parts of a drum brake having internal expand- 




Pigure 128. — Motor Cycle Type of Coaster Brake (New 
Departure). 



ing shoes are shown in Figure 132. The shoes are 
expanded by movement of the cam at the upper end 
of the operating lever and they are returned to a 
released position by the upper coiled spring. The 
operating lever is returned to its released position by 
the lower coiled spring. 

Another internal expanding brake is shown in Fig- 
ure 133. This brake is adjusted by removing the 



DRIVING PARTS 



229 



cotter pin 1, loosening the nut 2, then loosening the 
lock nut 3, and turning the screw 4 to the right. At 
5 is shown the adjustment for length of the pull rod. 
Figure 134 shows a brake that includes both an 
internal shoe and an external band. This brake is 




Figure 129. — Brake Applied to Rear Wheel Belt Pulley 
(Bowden). 

adjusted by removing cotter pin 1, loosening nut 2, 
and lock nut 3, and turning the screw 4 to the right 
in the manner similar to that used with the brake 
just described. Both adjustments for the pull rod 7 



230 THE MOTOR CYCLE HANDBOOK 




Figure 130. — Brake Applied to Rear Wheel Belt Pulley 
(Bowden). 



DRIVING PARTS 



231 




Figure 131. — Brake Applied to Front Wheel (Bowden). 



232 THE MOTOR CYCLE HANDBOOK 

are shown at the points 5 and 6. The external brake 
is adjusted by removing pin A, lifting screw B from 
the clevis whei e connected to A and turning B into G 
by screwing it to the right. The drum is shown at 
Z>. This brake is operated by a flexible wire held on 
the frame by the clamp E. Another construction of 



Figure 132. — Internal Expanding- Brake (New Departure). 

internal and external brakes is shown in Figure 135. 
Brake Adjustment. — If the motor cycle is driven 
carelessly and run close to the stopping point before 
shutting off the power, excessive use of the brakes 
will be made necessary and they may require adjust- 



DRIVING PARTS 



233 




Figure 133.— Adjustments for Internal Brake on Indian 

Scout. 



234 



THE MOTOR CYCLE HANDBOOK 



ment as often as once in every five hundred miles. 
If the rider is more careful and allows the machine 
to slow up through inertia the brakes may operate 
for four or five thousand miles between adjustments. 
Adjustment will often be found unnecessary if the 
operating parts, the pull rod ends and levers, are 




. •..■•- ,../.■,;■,;.■.■■. ■-.": '■■•;-:■■...■-■;:■■".■■' : :•'■ ."■:..■■'■■■•.". '. ■v'/r ■ - ' ■■■-■■'■.■'■■ ^' 






Figure 134. — Adjustments for Internal and External Brakes 

(Indian). 



cleaned and oiled so that the brakes will release fully 
and so that they may be easily applied. If the brakes 
squeak or grip the fault may often be overcome by 
applying a small amount of powdered chalk or talcum 
powder to the brake lining. The brake adjustment 



DRIVING PARTS 



235 



should always be tested after the chains or the driving 
belt have been tightened. 

With the machine fitted with both external and 
internal brakes, the external band should be used 
under all ordinary conditions because it is easier to 
keep the external brake in adjustment and when worn 




Figure 135. — Internal and External Brakes (Excelsior). 

out it is easier to replace the lining of this band than 
it is to perform similar operations on the internal 
brake. If the machine is fitted with a front wheel 
brake that member should be used only in an emer- 
gency and it should never be used on slippery roads. 
Engine as a Brake. — The brakes may be relieved of 



236 THE MOTOR CYCLE HANDBOOK 

a great deal of work by using the compression of the 
engine to retard the motion of the machine. With the 
ignition turned off, the clutch engaged, and the high 
speed ratio in use, the engine will exert a very con- 
siderable braking effect and will bring the motor cycle 
to a stop within a fairly short distance. If this same 
procedure is followed except for the use of interme- 
diate or low gear in place of high, the retarding effect 
will be increased greatly. In using the engine as a 
brake, a certain amount of flexibility may be secured 
by slipping the clutch which is then in effect, the 
brake. 

Before descending a steep hill it is advisable to 
engage high or intermediate gear so to be ready to 
use the engine to hold the machine in check. If the 
engine stops, do not attempt to start it while coasting 
by engaging the clutch with low or intermediate gear 
in use for the drive will be seriously strained or 
broken. 



CHAPTER VIII 
RUNNING GEAR 

The parts of a motor cycle which comprise the run- 
ning gear include the frame for supporting the power 
plant, the front forks, the rear suspension, the wheels 
with their hubs, and the tires. All of the parts of 
such a running gear with the exception of the wheels, 
spokes, and rims, are shown in Figure 137. 

General Lubrication. — The points at which lubrica- 
tion is required on a typical motor cycle are shown 
in Figure 136. The numbers indicate the following 
items and after each item is mentioned the kind of 
lubrication that is used. 

1. Rocker arms, grease or oil. 

2. Front hub, cup grease. 

3. Rocker arm pivot, oil. 

4. Head bearing, cup grease. 

5. Control joints. Follow these throughout machine. 

Machine oil. 

6. Spring pivots, oil. 

7. Springs. Spread leaves with screw driver and 

insert graphite grease. 

8. Brake lever pivots and clutch, oil. 

9. Seat post pivots, oil. 

10. Seat post, oil. Remove and grease occasionally. 

11. Saddle springs, oil. 

12. Rear hub, cup grease. 

237 



238 



THE MOTOR CYCLE HANDBOOK 




o 
o 

H 



O 

o 



.a 



3 



RUNNING GEAR 239 

13. Transmission, heavy oiL 

14. Compression release, oil. 

15. Starter pedal shaft, oil. 

16. Chain, graphite and tallow. 

17. Intake valve rocker arm, oil. 

18. Magneto or dynamo, oil. 

Front Forks. — A typical front fork construction 
with the handle bars attached is shown in Figure 138. 
For ordinary riding the front forks of motor cycles 
are almost always equipped with some form of spring 
to absorb the road shocks. One construction is shown 
in Figure 139. The hub of the front wheel is carried 
at the forward end of the rocker bars seen at the 
bottom of the two forks. The weight of the motor 
cycle is carried by the fork toward the left or rear 
of the machine. This weight bears down upon the 
rear end of the rocker bar and would tend to force 
the rear of the bar downward. Downward movement 
of the rear end of the bar moves the forward fork 
in such a way as to compress the coiled spring. The 
spring is designed and mounted in such a way that 
the downward motion of the load-carrying fork is 
supported so that the recoil also is carried by the 
spring. A design in which the spring consists of two 
parts is shown in Figure 140, one of these parts 
serving as a load-carrier while the other is used as 
a recoil. 

A front fork having two load-carrying spring, one 
on each side of the wheel and also two recoil springs 
carried in tubes with the load springs, is shown in 
Figure 141. The operation of this fork is similar to 
the one just described except that four separate 
springs are employed. 



240 



THE MOTOR CYCLE HANDBOOK 




o 

02 
U 

a> 


o 



c3 

PL* 



o 
U 



w 

u 
Q 



3 
be 



RUNNING GEAR 



241 



Care should always be exercised when removing any 
parts which hold coiled springs under compression 
for otherwise a sudden release of the spring may 
damage the mechanical parts or may even cause per- 
sonal injury. 




Fignre 138. — Single Spring- Front Fork (Harley-Davidson). 



A front fork design using a compound leaf spring 
is shown in Figure 142. The weight of the motor cycle 
is attached to the rear end of this spring while the 
spring is supported at its front end by a frame mem- 
ber running down to the hub. With such a design, 



242 



THE MOTOR CYCLE HANDBOOK 



additional recoil springs are not used because the 
friction between the spring leaves is sufficient to damp 
the rebound in much the same way as this friction 
acts in well designed automobile springs. 

Rear Suspension. — A commonly used design of 




Figure 139. — Front Fork Construction (Reading Standard). 



spring seat post is shown in Figure 143. A saddle is 
carried at the extreme left-hand end of the upper 
bar and the right-hand end of this bar is pivoted on 
the frame. Between the pivot and the seat, the bar 
is supported by a flange which is in turn carried by 



RUNNING GEAR 



243 



a coil spring within the frame tube. Downward motion 
of the saddle is resisted by the upper spring while the 
recoil is met by the lower spring. 

An application of this principle is illustrated in 
Figure 144. The tension of the springs in such a seat 
post should be made just stiff enough to prevent the 




Figure 140. — Front Fork With Compound Spring 1 (Excelsior). 



post from striking bottom on a bump. This tension 
is adjusted by the nut 2 which is held by the jam 
nut 1. The particular seat post illustrated is reached 
for adjustment by removing the pin 3, and loosening 



244 



THE MOTOR CYCLE HANDBOOK 



the nut 4 which clamps the tube at the point marked 5. 

A type of rear construction using leaf springs is 

shown in Figure 145. The weight of the motor cycle 




Figure 141. — Front Fork With Separate Shock and Recoil 
Springs (Harley-Davidson). 



is carried at the thick end of the springs and the 
other end is supported by a framework carried over 
the rear wheel. 



RUNNING GEAR 



245 




Figure 142. — Front Suspension With Leaf Spring (Indian). 



246 THE MOTOR CYCLE HANDBOOK 

FLEXIBLE WIRE CONTROLS 

The parts of a Bowden wire control are shown in 
Figure 146. The wire member consists of two prin- 
cipal parts, one a closely coiled and practically incom- 
pressible housing which is called the outer member, 
and the other, a wire threaded through the housing 
and which is called the inner member. In motor cycle 




Figure 143. — Spring Seat Post Construction. 

practice the outer member is anchored, usually at both 
ends, while the inner member is attached to a control 
lever at one of its ends and to the part to be operated 
at its other end. This wire control is used for operat- 
ing the ignition and carburetor controls, the compres- 
sion release, the brakes, and in some cases the clutch 
and transmission. 

In handling this type of control, care should be used 



RUNNING GEAR 



247 



to see that the inner member on leaving the end of 
the outer member is kept in an absolutely straight line 




Figure 144. — Spring- Seat Post Adjustments (Harley- 
Davidson). 



for the remainder of its length because otherwise there 
will be rubbing and friction between the two parts. 
Whenever the wire is withdrawn from the housing, 
the wire should be covered with grease before the 
two parts are again assembled. 



248 THE MOTOR CYCLE HANDBOOK 

WHEELS AND HUBS 

The construction of a front hub is shown in Figure 
147. The hub flanges are drilled with counter-sunk 




Figure 145. — Rear Suspension With Quarter Elliptic Springs 
(Indian). 

holes which receive the spokes. The flanges and barrel 
are supported by ball bearings of the cup and cone 
type. The cup is carried in the hub barrel while the 



RUNNING GEAR 249 

cone is adjustable by being fitted onto a threaded 
central portion of the hub as shown in the illustration. 
Such bearings are properly adjusted when they are 
just tight enough so that the wheel will spin freely 
and will come to rest with the tire valve at the bottom. 
A correct adjustment will allow a very slight shake 
of the wheel. 




Figure 146. — Parts of Bowden Flexible Wire Control. 

Cup and cone bearings are adjusted by loosening 
the lock nut and then turning the cone one way or 
the other, to loosen or tighten the bearing. The right- 
hand cone will usually have a right-hand thread, while 
the left-hand cone has a left-hand thread. By feeling 
of the wheel while turning the cone it may be quickly 
determined whether the bearing is being tightened 
or loosened. When the adjustment is thought to be 
correct the lock nut should be tightened and the 
adjustment again tested to make sure that tightening 
these nuts has not affected the bearing. Hubs are best 
lubricated with a light-bodied cup grease because oil 
will tend to work out past the packing washers. 



250 



THE MOTOR CYCLE HANDBOOK 



The spokes in motor cycle wire wheels always have 
a tendency to loosen, this being especially true in the 
rear wheel. The rear wheel should be examined after 
the first two or three hundred miles driving and then 
each thousand miles thereafter. The front wheel and 
spokes should be examined three or four times a year. 
Loose spokes allow the rim to get out of line and this 




Figure 147. — Front Hub Construction (Excelsior). 



causes wobbling, tire wear, and poor control. Eiding 
with poorly inflated tires tends to loosen the spokes 
and this practice also damages the rims by allowing 
them to become dented and out of shape. 

When examining the rim for alignment, the wheels 
should be slowly turned through a complete revolution 
and the rim should lie midway between the forks all 
the way around. It is best to have a rim trued up 
by an experienced mechanic because a novice will 
usually spend a great amount of time and will more 
often succeed in making matters worse than in rem- 
edying them. After a wheel is trued up by tight- 
ening or loosening the spokes, the spoke ends that 



RUNNING GEAR 



251 



protrude on the tire side of the rim should be cut 
off flush with the nipples. If it is found that spokes 
continue to break in a certain wheel, it indicates that 
they have all been strained and damaged and the 
entire set should be replaced. 




Figure 148. — Mounting- of Rear Hub. 



It is somewhat difficult to properly lace a set of 
spokes into a rim. Some of this difficulty, especially 
that found in positioning the spokes, may be overcome 
by tightly tying all of the spokes at each place where 



252 THE MOTOR CYCLE HANDBOOK 

two of them cross each other, before the old rim is 
removed. The nipples are then taken out and the 
entire set of spokes with the hub is removed from the 
rim. Nipples may then be stuck through the holes 
of the rim to be replaced and these nipples will be 
found to slant in different directions. The set of 
spokes may then be placed in position by seeing that 
each spoke slants in the same direction as a nipple into 
which it can be placed. 

When preparing to lace the spokes into a wheel 
the spokes should first be assembled in the hub. It 
will be found that the head of each spoke will fit prop- 
erly in the counter-sunk side of the hole and if this 
is watched the spokes cannot be wrongly placed. The 
work is started with eight spokes turned so that four 
of them have their heads up and so that the other 
four have their heads down. They are crossed so that 
the outside spokes will cross four others. If crossed 
in the wrong direction, the outside spokes will only 
cross three others. 

The outside spokes must run in a direction opposite 
to that of the inside spokes on the same side of the 
wheel, but they will run in the same direction as the 
inside spokes on the opposite side of the wheel. These 
first outside spokes will then run in a direction oppo- 
site to the outside spokes on the opposite side of the 
wheel. Before the spokes are entered in the rim, 
the angle of the punch holes of the rim should be noted 
and when the spokes are properly lined up it will be 
found that they lie in the same direction as the rim 
holes. All the nipples must fit properly into the 
counter-sinks of the rim and all the spoke heads must 
fit properly into the counter-sinks of the hub flange 
when lying in the correct position. 



RUNNING GEAR 



253 



The strength of a rear wheel may be increased and 
its alignment preserved by wiring the spokes together 
at the points where they cross one another. This 
practice may somewhat decrease the resiliency and 
easy riding qualities of the wheel. 




Figure 149. — Construction of Motor Cycle Tire Casing" 
(Goodrich). 



TIRES 



The tire is described as to size by mentioning its 
sectional diameter which is the distance through the 
tire from left to right and by mentioning its over-all 
diameter which is the height from the road surface to 



254 THE MOTOR CYCLE HANDBOOK 

the extreme top of the tread. Motor cycle tires are 
made in sections of 2J, 2|, 2f, 3 and 3| inches. The 
greatest number are in the 3 and 3^ inch sizes. Over- 
all diameters are 26, 27, 28 and 29 inches, most of 
them being either 26 or 28 inches. 

Motor cycle tires are of the clincher type as shown 
in Figure 149. Such a tire is held in the channels of 
its rim by the shape of the bead. Inside of the casing 
shown in the illustration is placed the inner tube and 
between the beads of the casing is placed a strip 
called the flap, this flap serving to prevent direct 
contact between the inner tube and the rim to avoid 
pinching of the tube. 

Motor cycle inner tubes may be made in either of 
two types. One is the endless tube similar to that 
used with automobile tires. The other is called a 
butt-end tube and is made in one long piece so that 
it may be inserted into the casing without taking the 
wheel from the frame. 

As described by the Goodyear Tire & Rubber Com- 
pany in their booklet, The Story of the Tire, there are 
two general methods of manufacturing motor cycle 
tires. In the eore-and-mold construction, the tire is 
built up in plies of rubber-coated fabric, cut on the 
bias, the plies being stretched onto an iron core. 

These tires are built of three or four plies. In 
building three-ply tires, after the first ply has been 
put on, the bead strips, which are made of a semi-hard 
rubber compound, are placed in position on the sides 
of the tire, then the second and third plies are pulled 
on and rolled down over these beads, after which a 
ply of tread gum is put onto the tire to cover it 
entirely on the outside. In four-ply tires two plies 
are put under the beads and two over. 



RUNNING GEAR 255 

On the larger sizes of motor cycle tires, a breaker 
strip coated with cushion rubber is placed between 
the last ply of fabric and the tread. This aids the 
union between tread rubber and fabric and distributes 
the shock of sudden bumps by providing an elastic 
cushion to spread the strain. 




Figure 150. — Motor Cycle Tire Construction (Goodyear). 

When the building of the tire is finished, and with 
the core still inside, it is placed into a mold. The 
mold is put into a heater press under hydraulic pres- 
sure and the tire is there vulcanized. After vulcaniza- 



256 THE MOTOR CYCLE HANDBOOK 

tion, the tire and core are removed from the mold 
and the tire pulled off the core. 

In the second method a drum is used, the surface 
of which is turned to take the outside of the tire 
flattened out. In building a tire on such a drum, the 
procedure is exactly the reverse of the core method. 
First, the tread rubber is placed on the drum, next 
the outside ply, then the middle ply, then the beads 
are set in place and finally the inside plies. The tire 
is thus in the shape of a flat band with the inside 
part of the tire on the outside. 

The tire is wrapped onto the drum with a long nar- 
row strip of wet cloth under tension, and the whole 
is rolled into a vulcanizer similar to that used for 
curing bicycle tires. After curing, the wrapping is 
removed from the drum and the tire stripped off and 
turned right side out. 

In many cases the tire is now finished and sent out 
in this shape. Some manufacturers take the tire in 
this shape and inflate it over an inner tube on a 
rim and put it back into the vulcanizer for a few min- 
utes to set it into the proper shape. Others shape the 
tire by wrapping it down on a core, thus giving the 
tire the shape cure. 

In Figure 151 the parts of a motor cycle tire are 
clearly shown. Number 1 indicates the plies of fabric 
which form the carcass; 2 shows where rubber gum 
is placed between the plies of fabric; 3 shows the 
layer of cushion stock between the plies of fabric 
and the carcass, also the breaker strip; 4 indicates 
the tread which is made of tough and resilient rub- 
ber; 5 indicates the side wall, and 6 indicates the 
beads which fit into the channels of the rim. 

Tire Removal and Replacement. — If a tube is to 



RUNNING GEAR 257 

be removed or exposed for repair without taking the 
wheel from the frame, the casing should be lifted on 
the side which is away from the drive chain or belt 
so that the tube will not be pinched by the drive 
when the wheel is revolved. Many tires are marked 
"Apply This Side Last and Remove It First." When 
such an instruction appears it should be heeded. 

After the tube has been repaired it should be care- 
fully replaced in the casing and if of the butt-end 
type, especial care should be exercised to see that 




Figure 151. — Parts of a Motor Cycle Tire (Firestone). 

the tube is not twisted for a twist will result in a 
blow out. The flap must be in good condition and 
carefully adjusted under the tube. After the casing 
bead is replaced the tire should be lightly inflated 
and the inside bead examined to make sure that no 
part of the inner tube has been pinched. 



258 THE MOTOR CYCLE HANDBOOK 

Tire Abuse. — The tread of the tire will be rapidly 
worn away if the wheel rims are out of true or if 
the wheels are out of line in the forks. Loose wheel 
bearings or bent forks will also result in quick tread 
wear. Too quick use of the brakes so that they slide 
the wheels, too quick acceleration in low gear, or high 
speed over rough roads with the resultant spinning of 
the drive wheel, will all result in great damage to 
the tires. 

It may sometimes be found that oil from the ex- 
haust is deposited on the outside of the casing and 
if this is found to be true, the oil should be wiped 
away with gasoline. 

Tires are greatly abused by incorrect inflation. A 
2f inch tire should be inflated to thirty-five pounds, 
a 3 inch tire to forty pounds, and a 3J inch to forty- 
five or fifty pounds. 

Tire Care. — Inner tubes should always be the same 
nominal size as the size of the casing in which they 
are to be used. A three-inch tube should not be used 
in a two and one-half inch casing because the tube will 
be wrinkled and creased. Neither should a small 
tube be used in a large casing because the rubber of 
the inner tube will be stretched so far that its life 
will be shortened. Soapstone, mica or graphite are 
used to prevent the inner tube from sticking to the 
inside of the case when it remains in place for a long 
time. 

It is poor economy to use an old inner tube or an 
inner tube that carries a great many patches inside 
of a new casing. Nothing is much harder on a casing 
than being run practically deflated, and an old tube 
always leaks at a fairly constant rate, even though 
the leak may be quite slow. 



RUNNING GEAR 259 

Before any attempt is made to put the casing on 
the rim, all rust, road dirt and other foreign matter 
should be removed from the metal parts with which 
the casing will come in contact. 

When removing a tire preparatory to repairing a 
puncture the tube should be marked to show which 
side was toward the right or left. Then, with the 
tube taken out of the casing, it may be pumped up 
until the leak can be found and with the position of 
the leak known, that part of the casing may be given 
a very careful inspection. 

Should a casing blow out on the road a temporary 
repair may be made with an inside boot, or rim-cut 
patch as it is often called. These patches are some- 
times placed inside of the damaged portion of the 
casing without the use of any cement because they are 
to be removed as soon as a permanent repair can 
be made. If the casing is too old to be worth vulcan- 
izing a semi-permanent job may be performed by 
cementing the blow-out boot into place. 

If a blow out has caused a large hole in the fabric 
of the casing an emergency repair can often be made 
by using an outside boot fastened by straps, hooks 
or leather lacings. Such a boot may be applied after 
the inner tube has been replaced or repaired, and 
after some form of reinforcement has been placed 
between the tube and the casing at the point of dam- 
age. 

In order to insure long life and freedom from 
trouble in the tires it is necessary that the rims be 
kept free from rust and from dents. With the casing 
removed, all parts of the rim which come in contact 
with the rubber should be thoroughly cleaned with a 
stiff wire brush or with emery cloth. Any dents or 



260 THE MOTOR CYCLE HANDBOOK 

bends should then be straightened, because these will 
cause chafing and eating away of part of the tire 
bead. After the rims are cleaned and put into proper 
shape the metal parts should be given a coating of 
some good rim paint. 



CHAPTER IX 

POWER ATTACHMENTS AND SIDE CARS 
BRIGGS & STRATTON MOTOR WHEEL 

The Briggs & Stratton unit consists of a four-cycle 
air-cooled engine attached to a driving wheel and 
fitted with the necessary accessories in ignition, car- 
buretion and lubrication to form a complete power 
unit. This power unit is attached along side the 
rear wheel of an ordinary bicycle and the controls are 
carried to the bicycle handle-bars. The outfit then 
acts as a traction device and drives the bicycle. The 
general construction is shown in Figures 152 and 153. 

One of the noticeable features of this power plant 
is found in the valve action. The inlet valve is of 
the automatic type. It is drawn open to admit the 
mixture by the suction of the piston descending on 
the inlet stroke. When the cylinder has become filled 
with gas and as the piston starts on its compression 
stroke, the inlet valve is closed with the assistance 
of a light coiled spring. The exhaust valve is of 
the mechanically operated type and is operated from 
a cam having four lobes. The camshaft runs at one- 
eighth of* the speed of the crankshaft so that one 
lobe comes underneath the valve-lifter at each second 
revolution of the crankshaft. The valve action is 
therefore the same as found in any other type of fomv 
cycle engine. 

261 



262 



THE MOTOR CYCLE HANDBOOK 



Lubrication is by a constant level circulating splash 
system. The lower part of the crankcase forms a 
reservoir from which oil is drawn by a plunger pump 
driven from an eccentric on the camshaft. The oil 




Figure 152. — Side Elevation of Briggfs & Stratton Power 

Plant. 

passes into the splash trough and its level is main- 
tained by an overflow. 

The Briggs & Stratton carburetor is shown in Fig- 
ure 154. The carburetor includes a non-adjustable 



POWER ATTACHMENTS AND SIDE CARS 263 




Figure 153. — End Section of Brigf&s & Stratton Power Plant. 



264 



THE MOTOR CYCLE HANDBOOK 



nozzle consisting of four parts; the nozzle itself, a 
ping, a coil spring, and a fibre washer. The throttle 
valve is of the piston type. 

The traction wheel is mounted on the end of the 




Figure 154. — Brig-gs & Stratton Carburetor. 



engine cam shaft. In order to distribute the wear 
on the tire that is caused by the power impulses, the 
wheel should be removed at the end of each five hun- 
dred to one thousand miles and its position should 



r» 



POWER ATTACHMENTS AND SIDE CARS 



265 




266 THE MOTOR CYCLE HANDBOOK 

be changed by removing the bolts which hold the 
traction wheel and advancing one space forward so 
that power impulses affect other parts of the tire. 

JOHNSON MOTOR WHEEL 

The Johnson motor wheel unit includes a two- 
cylinder two-cycle horizontally-opposed engine car- 
ried above the rear wheel of a bicycle and driving the 
rear wheel through a chain which runs over a large 
sprocket attached to the wheel rim. 

With this engine is used an unique type of magneto 
shown in Figure 155. The moving part of the mag- 
neto is the flywheel of the engine and contains the 
magnet, pole pieces and cam. The stationary part of 
the magneto is called the armature plate. It carries 
a large ignition coil and armature and a smaller light- 
ing coil and armature, a condenser in a metal tube and 
the breaker. Two thick rubber-covered wires with 
metal clips are used for ignition. A thin wire coming 
from near the center of the armature plate is a light- 
ing wire. The ignition and lighting systems are en- 
tirely independent of each other. 

Electricity is generated for both the ignition and 
lighting currents by revolving the magnet around the 
coils and their armatures. At the moment the pole 
pieces on the magnet pass the armature, the cam in 
the flywheel pushes the breaker blade and opens the 
points of the breaker which causes a spark at the plugs 
and also creates current for lighting. 

The breaker points should open one-sixty-fourth of 
an inch. By opening the small hole in the flywheel 
and turning the flywheel back and fourth, it may be 
seen whether the points are opening the correct dis- 



POWER ATTACHMENTS AND SIDE CARS 267 




268 



THE MOTOR CYCLE HANDBOOK 



tance. They may be adjusted with a magneto wrench 
through the inspection hole. 

After the breaker points are adjusted to the cor- 
rect distance, the timing may be adjusted. A timing 
line marked S is on the edge of the flywheel and a 
like mark is on the back of the armature plate. These 
two marks should be brought exactly opposite each 
other by turning the flywheel. While looking through 




Fig-ure 157. — Cyclemotor Belt Pulley Attachment. 



the small hole in the flywheel, the flywheel may be 
turned back and forth, and it may be seen if the 
points of the breaker are just starting to open when 
the timing marks on the edge of the flywheel and the 
back of the armature plate are opposite. If they are 
not just opening at that time, the two screws holding 
the breaker plate are slightly loosened and the breaker 
plate is moved until the breaker points just start to 
open when the timing marks are opposite each other. 



POWER ATTACHMENTS AND SIDE CARS 



269 




270 



THE MOTOR CYCLE HANDBOOK 



The usual electric bicycle lamps may be used for 
both head and tail lights. If both head and tail lights 
are used, the bulb for the head light should be 2.8 
volts and for the tail light 4 to 6 volts. If only one 



- -<■*. ''%L 




%k'^5fcS^JJ,^ 


vftlf 


:, i 




Figure 159. — Side Car Running Gear (National). 

light is used, the bulb should be 2.8 volts. To connect 
the lamps with the lighting coil, the wires from both 
lamps are connected to the light wire which comes 
out of the magneto near the center. If double con- 
tact lamps are used, one lamp wire is grounded by 



POWER ATTACHMENTS AND SIDE CARS 271 

attaching it securely to a metal part. If electric lights 
are not used, the lighting wire from the magneto is 
twisted securely out of the way. 

THE CYCLEMOTOR 

In Figure 156 is shown the power plant of the 
Cyclemotor. This consists of a single-cylinder two- 




Fig-ure 160. — Mounting- of Side Car Wheel (Rogers). 

cycle engine of one horsepower which is designed to 
reach speeds as high as three thousand revolutions a 
minute. The power plant is carried within the dia- 
mond of a bicycle frame. Power from the engine 
crankshaft is carried to a belt pulley through a chain 



272 THE MOTOR CYCLE HANDBOOK 

and this same chain serves to drive the magneto. From 
the belt pulley power is carried to the rear wheel 
through a V type leather belt. 

SIDE cars 

Side cars for carrying passengers or merchandise 
may be fitted to any of the motor cycles in the heavy- 




Figure 161. — Side Car Suspension (Excelsior). 

weight class. In some cases the engine for a side 
car outfit has a larger compression space and there- 
fore a lower compression pressure than the regular 
type. This makes the engine better able to handle 
hard pulling at low speeds, although it somewhat 
reduces the maximum speed available. 

A motor cycle for use with a side car should have 



POWER ATTACHMENTS AND SIDE CARS 



273 



a comparatively low gear in high speed, this ratio 
usually being at least five-to-one. With high geared 
machines there is considerable danger of overheating 
and a more or less serious lack of power. 

It is necessary that a side car be properly aligned 
with the motor cycle and before attaching the side car, 
the frame, the forks and the wheels of the motor cycle 
should be carefully lined up. 
- When a side car is to be attached, a straight edge 




Figure 162. — Two-Passenger Side Car (Harley-Davidson). 

should be laid along both wheels of the motor cycle 
and a similar straight edge should be laid along the 
side car wheel. While the motor cycle is practically 
upright, the side car should be adjusted until the 
straight edges are exactly parallel with each other. 
The side car should be so attached that the top of the 
side car wheel leans slightly away from the motor 
cycle or so that the top of the motor cycle wheel 
leans slightly away from the side car. 



274 



THE MOTOR CYCLE HANDBOOK 



With the side car in proper alignment, tire wear 
will be reduced to a minimum and driving will be 
extremely easy. If the side car wheel leans toward 
the machine or the machine toward the side car, the 
motor cycle tires will wear on the right hand side 
instead of the center and on the side car the tire will 
wear on the left hand side. The steering will also be 
interfered with. With the side car leaning away 




Figure 163. — Side Car With Top and Storm Front (Excelsior). 



from the machine, the tires will be worn on the out- 
side instead of in the center and their life materially 
shortened. In this position, the steering will also be 
affected and there will be a side-drag, most noticeable 
on high-crowned roads. With a side car properly 
aligned, the machine will travel straight ahead for one 
hundred feet or more on a level road when running 
at moderate speed and without guidance. 



POWER ATTACHMENTS AND SIDE CARS 



275 



03 



p 

o 
p 



O 

P 



P 



d 
P 
< 




276 TKE MOTOR CYCLE HANDBOOK 

The side car fastenings, the ball and socket joints, 
and all nuts and bolts should be kept properly ad- 
justed and tightened. Ball and socket joints should be 
lubricated at frequent intervals because otherwise 
they will rust solid and become bent or broken. 

A machine carrying a side car should not be over- 
loaded. It has been decided that five hundred pounds 
is the normal carrying capacity of the motor cycle 




Figure 165. — Tandem Attachment (Fentress-Newton). 

and side car combined. This would mean that the 
weight of the driver combined with the weight of the 
side car and its passenger or passengers should not 
exceed five hundred pounds. This limit applies to 
ordinary riding conditions but in driving over very 
rough or hilly roads the weight should be reduced. 
While a motor cycle and a side car will pull a heavier 
load than that mentioned, it will be done only at the 



POWER ATTACHMENTS AND SIDE CARS 277 

expense of mechanical life and of high maintenance. 
In driving a side car around a right-hand corner 
the clutch should be disengaged and should be al- 
lowed to engage again at the turn. The motor cycle 
will turn around the side car wheel. In turning to 
the left, the corner should be approached with the 




Figure 166. — Back Rest Attached to Saddle (Fentress- 
Newton). 

clutch disengaged and it should be kept disengaged 
until the turn has been completed. If this method 
is not followed the side car will tend to skid to the 
right when making a left-hand turn and will tend to 
rise from the ground when making a right-hand turn. 



CHAPTER X 

MOTOR CYCLE REPAIRS 

Because of the extreme accuracy of workmanship 
and the close limits within which parts are fitted and 
adjusted, it is not advisable for anyone except an 
experienced mechanic to make anything other than 
minor repairs and service adjustments. It has already 
been mentioned that the motor cycle is a finer piece of 
mechanism than the average automobile and for this 
reason, while a motor cycle mechanic would do good 
work on an automobile, it does not follow that an 
automobile repair man would always do good work 
on a motor cycle. 

The brief instructions given in the following pages 
assume that the one doing the work has a knowledge 
of general shop practice and is familiar with the 
proper use of ordinary shop tools and equipment. 
The information that is given is intended more as a 
series of cautions applying especially to motor cycle 
work than as a series of instructions which may be 
followed by a novice. To give a complete explanation 
of good motor cycle repairing would require that a 
treatise on shop work be included. 

While most of the following material applies 
equally well to any type of motor cycle, the greatest 
attention has been given to work involved with han- 
dling the twin-cylinder, four-cycle. V type engine 
working in connection with a clutch and gear-set 

278 



MOTOR CYCLE REPAIRS 279 

through the usual forms of drive. This will of course 
allow the reader to handle two-cycle machines, single- 
cylinder machines, and machines without gear-sets, 
because those variations in practice are secured by 
omitting some of the parts of the more complicated 
heavy-weight outfit. 

Good repair work in any field can be done only if 
the workman has access to good tools of the neces- 
sary variety. Except for a few running adjustments 
very little can be done with the tool kit furnished 
with the motor cycle. A mechanic's outfit should 
include a complete set of end wrenches and a fairly 
good selection of the commonly used sizes of socket 
wrenches. In many cases it will be desirable to secure 
special wrenches for fitting some of the less accessible 
bolts and nuts and also special wrenches for handling 
some types of hubs as we.l as for electrical devices. 

Some of the following work will call for microm- 
eters, both outside and inside, with fittings that allow 
them to measure work between three and four inches 
in diameter. It will also be necessary to have thick- 
ness gages, expansion reamers, gear pullers, copper 
hammers, and such machine shop tools as are gen- 
erally available where work of this nature is to be 
handled. 

CYLINDERS 

When making ready to remove the cylinders from 
the crankcase it is of course necessary to disconnect 
practically all of the fastenings which attach to the 
cylinders. Especial care will be required in removing 
the exhaust pipe nuts because if they bind and are 
jerked loose with a large wrench, breakage of the 
cylinder casting may result. These nuts should be 



280 THE MOTOR CYCLE HANDBOOK 

soaked with kerosene for some little time before they 
are to be removed. While the wrench is applied and 
some strain put upon it, the nut should be tapped with 
a hammer. It may sometimes be necessary to run 
the engine in order to warm the parts before this 
connection can be taken apart. 

The pistons should be brought to the bottom of 
their strokes before the cylinder is lifted off. The 
cylinder casting can then be raised while carefully 
rocking it or while slightly turning the drive sprocket 
so that the piston slides out easily. 

When the cylinder is to be replaced it should be 
seen that the gaskets between the cylinder flange and 
the crankcase are unbroken. If they have been 
jammed or torn, new gaskets should be fitted. Should 
the engine have been fitted with plates between the 
cylinder and crankcase in order to reduce the com- 
pression pressure, a gasket should be put above and 
another below these plates. 

After the cylinder has been removed it can be 
examined for the condition of the inside surface. If 
in good shape the cylinder walls will be found per- 
fectly smooth and there will be no scratches, burned 
spots, or score marks. If the machine is comparatively 
new some of the marks of the grinder may still be 
visible. 

If it is found that the cylinder is only slightly scored 
it may be put into fair shape by lapping, but if the 
score marks are at all deep, that is, if the marks 
are four or five thousandths of an inch below the sur- 
face, the cylinders should be reground. If the cylin- 
ders have previously been reground and again show 
deep score marks they will have to be replaced with 
new ones. 



MOTOR CYCLE REPAIRS 



281 




Figure 167. — Measuring- Cylinder "Bore With Inside Microm- 
eter. (Courtesy of Harley-Davidson Motor Co.) 



282 THE MOTOR CYCLE HANDBOOK 

In order to measure the wear in the bore of the 
cylinder it will be necessary to use an inside mi- 
crometer as shown in Figure 167. The bore cannot be 
accurately measured with ordinary calipers or even 
with a gage, because it will be found that the wear 
has caused the cylinder to become larger at the upper 
end than at the lower. When calipering the cylinder 
bore measure it at several points between top and 
bottom and also try the micrometer at different angles 
in order to determine whether or not the cylinder is 
out of round. 

Carbon Removal. — While the cylinders are off the 
engine the collections of carbon can be removed from 
all points inside the combustion space by means of 
specially formed scrapers. At this time the carbon 
can also be removed from the top of the piston, from 
inside of the piston, and from the piston-ring grooves. 
This cleaning should be performed once in each three 
or four thousand miles running and in no case should 
it be delayed for over a year. It is seldom, if ever, 
safe to burn the carbon out of motor cycle cylinders 
with oxygen as is a general practice with automobile 
engines. 

It will be found in a number of cases that the 
cylinder head is separate from the barrel and held 
in place by studs or bolts. This practice is followed 
more as a measure to allow good machining inside a 
cylinder than as a means of allowing ready access 
to the combustion space. It will usually be best to 
handle all types of cylinders as if they were made in 
one piece, that is, remove them from the crankcase 
when the carbon is to be cleaned out. 

The frequency with which it is necessary to remove 
the carbon depends in great measure on the oil feed 



MOTOR CYCLE REPAIRS 283 

because too much oil will invariably result in con- 
siderable deposits of soot which are injurious in that 
they cause more rapid wear of the piston and cylinder 
walls. 

The necessity for carbon removal can be postponed 
by injecting kerosene into the combustion space about 
once in each seven hundred and fifty to one thousand 
miles of running. While the engine is still hot from 
running, the spark plugs can be removed or the 
priming cups may be used to inject a liberal quantity 
of kerosene into each cylinder of the engine. If the 
work is to be properly done the oil line should be 
disconnected from the crankcase and a supply of kero- 
sene placed at this point also. With the spark plug 
wires still removed the engine should be rapidly 
cranked so that all of the parts are washed clean. 
The drain plug in the bottom of the crankcase can 
then be removed and the kerosene drained away, the 
plug replaced and normal supply of oil put into the 
case. Again crank the engine a few times so that the 
oil is distributed, connect the spark plug wires and 
the machine is ready for operation. 

When the carbon is removed from the engine it 
would be advisable to inspect the muffler and exhaust 
pipe because there may be a considerable loss of power 
due to the accumulation of carbon that forms in these 
parts. 

PISTONS AND PISTON PINS 

When the pistons are exposed all of their carbon 
should be removed, the rings should be taken out and 
their grooves should be cleaned. It will then be pos- 
sible to determine whether the pistons show excessive 



284 



THE MOTOR CYCLE HANDBOOK 



wear or whether they are scored. If work is to be 
done on the piston itself or on the connecting rod or 
its bearings, the pistons will be removed by taking 




Figure 168. — Extracting Piston Pin. (Courtesy of Harley- 
Davidson Motor Co.) 



out the piston pins but unless such work is necessary 
it will be best to allow the piston to remain attached 
to the rod. If the engine has more than one cylinder 



MOTOR CYCLE REPAIRS 285 

the pistons should be carefully marked as to their 
position in the engine because it very seldom will 
be found that a piston from one cylinder will make a 
proper fit in any other cylinder. 

The piston pin should be removed and replaced by 
the use of some such tool as shown in Figure 168. 
This tool is designed to give the walls of the piston 
proper support while the pin is forced out of or into 
its place by means of a screw. Piston pins are often 
handled by driving them with a punch and hammer 
but such a practice will almost always throw the 
connecting rod out of line and will make the piston 
itself very much out of round. Begardless of the 
method used in handling the pins it should be borne 
in mind that the piston is somewhat delicate and 
may be broken quite easily by the application of too 
much force. 

If the engine is to be made quiet the pistons must 
be a good fit in the cylinders. If the pistons are a 
loose fit they will slap, while if they are too tight 
they will cause a tapping noise due to the pistons 
sticking at the top and again at the bottom of the 
stroke so that the slack in the connecting rods is 
taken up at each of these positions. The micrometer 
should be used as in Figure 169 to measure the diam- 
eter of the piston at its low T er end about one-half inch 
from the bottom. Measurements should be taken at 
several positions around the cylinder so that it can 
be noted whether the walls are out of round. If the 
piston is found to be more than ten thousandths of 
an inch smaller than the upper end of the cylinder 
bore, it will be necessary to fit a new over-size piston. 
If it has been found w r hen measuring the cylinder, that 
the upper part cf its bcre is larger than the lower 



286 



THE MOTOR CYCLE HANDBOOK 



end, it will be necessary to regrind the cylinder and to 
fit over-size pistons. 

In selecting a new piston, the small diameter of 
the cylinder should be found first and a piston should 
be used whose large diameter is very close to three 




Figure 169. — Measuring- Piston Diameter With Outside Mi- 
crometer. (Courtesy of Harley-Davidson Motor Co.) 

thousandths of an inch smaller than the cylinder 
diameter. With such a fit, lapping will not be neces- 
sary. Should the fit be made much closer than three 
thousandths of an inch, the new piston with its rings 
will have to be lapped into the cylinder, which is a 
shop operation. 



MOTOR CYCLE REPAIRS 



287 



The piston pin should be a running fit in its bush- 
ings and with the pin in place the piston should have 
about one-sixteenth of an inch end play along the 
pin. Should a new piston pin bushing be fitted it will 
be necessary to ream it with very light cuts as in 




Figure 170- 



-Reaming- Piston Pin Bushing. 
Harley-Davidson Motor Co.) 



(Courtesy of 



Figure 170. The bushing should be reamed only large 
enough so that the weight of the piston will turn the 
parts when the piston and connecting rod are held 
horizontally. Should an over-size piston pin have 
been fitted to the bushing it will be necessary to ream 



288 THE MOTOR CYCLE HANDBOOK 

the piston openings to take this over-size pin, when the 
construction is such that the pin is stationary in the 
piston. 

After the piston and pin have been assembled, the 
flywheels should be turned imtil the crank pin is at 
its lowermost point. The pistons can then be exam- 
ined to see that they are approximately centered with 
the cylinder opening into the crankcase. It must be 
possible for the piston to take an absolutely central 
position in this opening without causing the bosses 
in the piston walls to rub against the piston pin bush- 
ing or without allowing the connecting rod to strike 
bushings carried in the pistons. If the pistons cannot 
be centered in these openings, and if it is known 
that the connecting rods are in line, it will be neces- 
sary to remove a little metal from either side of the 
piston pin bushings or else it may be possible to move 
the bushings a little in the direction that will al^ow 
more clearance. The pistons shouM never be brought 
to a center by putting two offset bends in the connect- 
ing rad. 

After the pistons have been attached to the connect- 
ing- rods and centered with the crankcase openings, 
they should- be measured for roundness. The outside 
micrometer should be used to take measurements at 
several points around the lower end of the piston 
walls. If the piston is found to have high spots these 
may be removed by carefully striking them with a 
hammer handle or piece of wood. In some cases the 
piston can be made round by the use of a clamp. 
Failure to make the pistons almost absolutely cylin- 
drical will be very liable to cause overheating and a 
loss of power. After the pistons have been made 
round they should be handled with care and shoukl 



MOTOR CYCLE REPAIRS 



289 



not be allowed to strike the connecting rod or crank- 
case. 

Squaring the Pistons. — The axis of a piston must 
be absolutely true with the axis of its cylinder because 
otherwise the piston will be tipped so that there will 




Figure 171. — Connecting- Rod Construction of Twin-Cylinder 
Opposed Engine (Harley-Davidson). 



be a considerable loss of power and more wear at 
one point on the piston than at other points. 

The pistons are tested for this condition by seeing 
that they are square with the finished surface of the 



290 



THE MOTOR CYCLE HANDBOOK 



crankcase against which the cylinder flange fastens. 
Misalignment of this nature is sometimes found by 
using two steel squares with one of their legs resting 
on the crankcase while the other is laid along the 
piston wall. 















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Figure 172. — Squaring- Pistons With Surface Plate. (Cour- 
tesy of Harley-Davidson Motor Co.) 



The more generally used method of testing the 
clearance of the pistons is to check them directly 
against the crankcase surface by the use of a squaring 



MOTOR CYCLE REPAIRS 291 

plate as shown in Figure 172. This plate has its top 
and bottom surfaces perfectly parallel with each other 
and it is provided with an opening through which 
the connecting rod can pass. With the plate resting 
on the crankcase the lower end of the piston is brought 
down against the top of the plate. If the piston is 
found to bear evenly on both sides, it is square. The 
contact of the piston with the plate can be tested by 
placing very thin pieces of paper at opposite points, 
when it should be just as difficult to draw the paper 
away from one side as from the other. 

The pistons should be tested for squareness first 
with the crank pin in its forward position and then 
with this pin toward the rear. Should it be found 
that one side of the piston does not rest on the plate 
with the crank pin forward, while the opposite side of 
the piston does not rest on the plate with the crank 
pin at the rear, it indicates that the connecting rod 
is twisted. If the failure to touch the plate is found 
to be on the same side of the piston regardless of the 
position of the crank pin, it indicates that the con- 
necting rod is bent to one side or the other, but not 
twisted. 

The pistons are made square by either bending or 
twisting, or by both bending and twisting the con- 
necting rod as shown in Figure 173. This work is 
continued until both sides of the piston rest squarely 
on the plate. 

PISTON RINGS 

The piston rings should be examined to see that 
they have a full bearing against the cylinder walls 
all the way around the outside of the ring. Should 



292 



THE MOTOR CYCLE HANDBOOK 



some points be found burned or scored the ring should 
be replaced with a new one. The rings are subjected 
to a great deal of heat and it may be found that some 




Figure 173. — Truing- Connecting Rods. (Courtesy of Har- 
ley-Davidson Motor Co.) 



of them, especially near the top, will have lost their 
resiliency so that they can no longer make a gas-tight 
fit. 

The gap between the ends of the ring is for the 
purpose of allowing expansion under heat and for 






MOTOR CYCLE REPAIRS 293 



allowing the ring to follow the variations in the cyl- 
inder bore. This gap can be measured by removing 
the ring from the piston and placing the ring squarely 
into its cylinder. If the gap is more than five-hun- 
dredths of an inch, it will allow a serious loss of com- 
pression. The proper gap for a new ring is about 
twenty-thousandths of an inch. 

It may be necessary to file away some metal from 
the ends of the ring in order to secure the correct 
opening, but if the ring is originally of too large 
diameter and the ends are filed away in order to 
allow it to enter the cylinder, the face of the ring 
will not bear against the cylinder walls and it will be 
impossible to make a proper fit. After the ends of 
the ring have been filed they should be pressed to- 
gether to make sure that they meet at all points, in 
other words, to make sure that the filing w T as properly 
done. 

The rings should be tested for their fit in the piston 
grooves and there should be only the slightest freedom 
between the top and bottom of the ring and the top 
and bottom of the groove. If it is known that a 
ring is of the correct width and it still shows consid- 
erable looseness in the groove, it indicates that the 
grooves are worn and it will be necessary to replace 
the piston. It is assumed that the ring grooves have 
been carefully cleaned of all carbon before any at- 
tempt is made at fitting. 

When it comes time to replace the cylinder over the 
piston with the rings in place, the gaps in the several 
rings should be placed at widely separated positions 
around the cylinder walls. Care must be used in 
dropping the cylinder into place that the rings are 
not jammed and broken. 



294 



THE MOTOR CYCLE HANDBOOK 




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MOTOR CYCLE REPAIRS 295 

ROLLER BEARINGS 

Roller bearings are quite generally used at the 
lower end of the connecting rods in motor cycle 
engines. This type of bearing is also frequently used 
for one or both of the bearings in the crankcase 
which support the flywheels, as in Figure 175. 

While the roller bearings should be examined when 
the engine is being taken apart for any reason, their 
adjustment should" not be disturbed unless it is really 
necessary. The fit of the roller bearing at the lower 
end of the connecting rod can be determined by noting 
the up and down play of the rod while the crank 
pin is at its upper position and while the rod is 
being held straight up. If any up and down play can 
be felt with this movement, the bearings should be 
tightened. The fit of the roller bearing may also be 
tested by the side play of the upper end of the con- 
necting rod. 

Roller bearings of this type are generally refitted 
by substituting over-size rollers for those that have 
become worn. " While this is true for the type of 
bearing in which the rollers may be easily inserted 
or withdrawn, it may sometimes be necessary to renew 
other parts of the bearing in addition to the rollers. 
Whether the work is done by fitting new rollers or 
by renewing the complete bearing, the final fit should 
be such that there is no perceptible play while the 
parts can still be turned around each other with per- 
fect freedom. 

FLYWHEELS 

In fitting a tapered crank pin into a pair of fly- 
wheels, the parts must be drawn very tightly to- 



296 



THE MOTOR CYCLE HANDBOOK 




Figure 175. — Connecting- Rod With Roller Bearing's and 

Crankshaft With Roller Bearings and Ball 

Bearing (Precision). 



MOTOR CYCLE REPAIRS 297 



have no end play, but are cramped when the crank 
pin is tightly secured, it may be necessary to use a 

I new pin or to change the fitting of the connecting rod 
bearing. In some cases this trouble may be caused 
by the taper holes in the flywheels being too large. 
Whenever a key is used in connection with tapered 
shaft fittings, the key should have a bearing along 
its sides in both the key-ways, but it should not have 
a bearing in the bottom of both key-ways because this 
would prevent the tapers from making a correct fit. 
The key itself is seldom depended on to carry the 
drive, for this work can better be done by the friction 
of the tightly drawn tapers. 
After the crank pin is fitted in the flywheels it is 
necessary to bring the two opposite flywheel shafts 
or crankshafts into exact line with each other. It 
is not necessary to true the rims of the flywheels or 
to true the faces of the flywheels, but it is necessary 
to true the shafts. The work can be correctly handled 
by mounting the flywheel and shaft assembly between 
centers made for this purpose as in Figure 176 or 
between the centers of a lathe. Indicators of the 
type shown can be placed in contact with each of the 
shafts so that when the assembly is turned, the indi- 
cators will show any misalignment. If standard lathe 
indicators are used in place of the kind illustrated, 
it will be best to lay a piece of clean white paper 
underneath the work and then to sight between the 
indicators and the shafts while the flywheels are 
turned. 

When the high spots are located the shafts are 
turned until these spots are uppermost and then with 
the copper hammer the flywheel attached to the shaft 



298 



THE MOTOR CYCLE HANDBOOK 



being straightened is struck squarely on top. If the 
flywheel is of the spoked type it should not be struck 
between two spokes and if the high point comes in 
such a position the wheels should be struck at two 
places directly over the spokes which are at each side 
of the high point. It is best to true both the shafts 




Figure 176. — Truing- Crankshafts. (Courtesy of Harley- 
Davidson Motor Co.) 



at the same time, that is, one of them should not be 
made absolutely true before work is begun on the 
other one because truing the second shaft will very 
often throw the first one out of line. After the shafts 
have been properly aligned, the assembly must be 
handled with great care until it is mounted in the 
crankcase. 






MOTOR CYCLE REPAIRS 
THE CRANKCASE 



The crankcase of the motor cycle engine should 
never be taken apart unless it is necessary to do so in 
order to make repairs. The halves of the crankcase 
are very carefully fitted to make an oil-tight joint. 
They should not be wedged apart because such prac- 
tice will damage the machined surfaces and will prob- 
ably result in an oil leak. 

When the flywheels with their shafts are mounted 
in the crankcase bearings it is necessary that the 
bearings be exactly in line with each other because 
otherwise the flywheel shafts which have already been 
carefully lined up, will bind and cause a great loss 
of power. 

The two halves of the crankcase should be put on 
over the flywheel shafts and bolted together at several 
points. It should then be possible to turn the fly- 
wheels freely. If they are not free it will be neces- 
sary to line up the parts of the crankcase which carry 
the bearings. This is done by passing a lining-up bar 
through one bearing and to the other, using special 
bushings in the work. When it is thus found in which 
direction the bearings are out of line the bar is partly 
withdrawn and the crankcase is slightly sprung as 
shown in Fgure 177. It may sometimes be necessary 
to ream the crankcase bushings as shown in Fig- 
ure 178. 

After the flywheel shafts have been fitted into the 
crankcase bearings the halves of the case are again 
removed and, their joints having previously been 
cleaned thoroughly, these joints are reshellaced, the 
gasket is put in place, the parts are reassembled, and 
finally bolted together. If the old gasket was un- 



300 



THE MOTOR CYCLE HANDBOOK 



broken it will not be necessary to replace it with a 
new one. 

When a motor cycle engine is assembled, all of the 
parts must move with perfect freedom. An engine 







Figure 177. — Truing Crankcase Bushings. (Courtesy of 
Harley-Davidson Motor Co.) 

should never be put into use with any of the parts 
binding even in the slightest degree as might be 
allowable in the case of an automobile engine. Motor 
cycle engines run at extremely high speeds and be- 



MOTOR CYCLE REPAIRS 



301 



cause of this fact neither looseness or binding is per- 
missible. 



VALVES 



The valves and the valve mechanism are subjected 
to many forms of trouble. While making an exam- 




Figure 178. — Reaming- Crankcase Bushings. (Courtesy of 
Harley-Davidson Motor Co.) 

ination of this part of the engine it should be noted 
whether either the inlet or exhaust valves tend to 
stick or bind in some positions. If this condition is 
found it is probably due to bent stems or to an ex- 



302 THE MOTOR CYCLE HANDBOOK 

eessive accumulation of carbon. Stems can be tested 
for straightness by rolling them along a perfectly 
flat surface. A valve stem should have only sufficient 
clearance in its guide to allow it to work easily. The 
proper clearance for an inlet valve stem is about two- 
thousandths of an inch while the clearance for the 
exhaust valve stem can be four- or five-thousandths. 
If the guide or the valve stem is badly worn there 
will be an air leak and the mixture will be affected. 

The valve stem, the valve face, and the seat in the 
cylinder should all be examined to see that no shoul- 
ders or ridges have been formed because this would 
result in holding the valve off its seat under some 
conditions. Should the engine have been run very 
hot at any time it is quite possible that the valve 
.head and the upper end of the stem may have been 
warped. 

In making an examination of the valve operating 
parts, such as shown in Figure 179, it should be seen 
that none of them stick and that there are no flat 
or binding rollers. If the guides for the valve-lifters 
are badly worn the engine will be noisy. 

The meshing of the timing gears determines the 
valve timing and the correct position is usually in- 
dicated by corresponding marks on or between the 
teeth of the large and small gear, these marks when 
registering with each other bringing the gears into 
proper relation. 

Compression. — Lack of compression in an engine 
almost always indicates that the valve faces and seats 
are pitted or carbonized and that they need grinding 
or refitting. The compression may be tested by slowly 
cranking the engine and by noting the resistance to 



MOTOR CYCLE REPAIRS 



303 



turning that is encountered during two full revolu- 
tions. As each cylinder is brought to its compression 
stroke, there should be a considerable increase in the 
effort required to operate the starter and at each of 
these points there should be a springiness due to the 




Figure 179. — Valve Lifter Adjustments (Precision). 



compressed gas in the cylinder. It should be possible 
to crank through a part of a revolution several times 
and to have the starter spring backward each time 
pressure is released. In case points of compression 
seem to be passed without any great resistance, it will 
probably be necessary to grind the valves. 



304 



THE MOTOR CYCLE HANDBOOK 



The trouble may be located in a certain cylinder 
by removing the spark plugs or by opening the pet 
cocks of the others. Each cylinder may be tested in 
this manner and if one of them allows the engine to 




Figure 180.- 



-Point at Which Oiling- Prevents Wear of Valve 
Mechanism (Harley-Davidson), 



be turned through two revolutions with little or no 
resistance, that cylinder is losing compression. 

Loss of compression does not always result from a 
poor valve seating because such leakage may come 



MOTOR CYCLE REPAIRS 305 

from loose spark plugs, loose priming cups, scored 
cylinders, poorly fitted rings, and similar faults. 

Valve Grinding— li the engine has its valves in 
side pockets with a valve cap and screw plug directly 
above the valve, it may be possible to insert a screw 
driver or a forked rod through the spark plug or pet 
cock opening in the valve cap and turn the valve on 
its seat through several revolutions. The valve face 
is polished by this turning, and any small particles 
of carbon may possibly be removed so that regrmding 
will be made unnecessary. 

If after polishing the valves by turning them on 
their seats only a slight leak of compression remains, 
the engine may be run for several days with the valve 
lifter adjusted quite loose. This excessive clearance 
will allow the valves to pound into place on their seats 
and will very likely result in a return of normal 
compression. 

Removing the Valves.— Two principal types ot 
valve mounting are employed. The valves may be 
in side pockets and covered by plugs or caps above 
them, as in Figure 181. By removing these caps the 
valves may be withdrawn through the top of the cyl- 
inder. Overhead valves are placed in cages which 
are themselves removable, while the springs are still 
carried by the cages. 

With engines having pocketed valves it will be 
necessary to remove the valve spring from around 
the stem by methods whose exact application is de- 
termined by the construction used. It may some- 
times be found that the cages of overhead valves resist 
attempts to remove them from the cylinder casting. 
In such an event it will be best to pour a liberal 
quantity of kerosene around the cage before using 



306 THE MOTOR CYCLE HANDBOOK 

any amount of force to pull it out of place. A light 
hammer tap on the upper end of the valve stem while 
the spring is still in place may loosen the cage suffi- 
ciently for it to be taken out. 

Ee facing and Eeaming.—Ii the valve face has be- 
come concave clue to excessive wear or to a great 
number of grin dings, or if the face is found to be 
very badly scored or pitted, it will be next to im- 
possible to secure good results by simple grinding. 
In this case the valve should be replaced with a new 
one or else the old one should have a new face made 
at the proper angle by placing it in a lathe or refac- 
ing tool and removing a slight cut. 

Should the valve seat be found badly scored or 
pitted, or should it have assumed a convex form, it 
will be necessary to restore the correct seating by 
means of a reamer constructed for this work and 
used as shown in Figure 182. 

When using the reamer it may be found that the 
teeth do not cut when the tool is first put into action. 
This is because it may be very difficult to force the 
reamer through the scale that has been burned onto 
the valve seat. If a slight additional pressure is ex- 
erted on one side of the reamer, that is, if the tool is 
tipped, the scale can be cut through with one revolu- 
tion. The work is finished by giving the reamer a 
few turns under light pressure. 

Grinding Methods. — After the valve has been re- 
moved and cleaned ready for grinding, it is necessary 
to use a very small quantity of valve grinding com- 
pound applied to the face of the valve with the finger 
tip or a knife blade. It is usually best to use the fine 
grade such as recommended for finishing. 

A short length of light-weight coil spring should 



MOTOR CYCLE REPAIRS 



SOT 



be placed around the valve stem and brought up 
against the head. With the spring in place and the 
compound evenly distributed over the face, the valve 
may be dropped back into place so that it rests on its 




Figure 181. — Removing Pocketed Valve (Indian). 

seat. The coil spring is used so that the valve face 
may be allowed to rise from the seat at intervals 
during the grinding operation. 

Bv means of a screw driver or forked rod, or some 



308 



THE MOTOR CYCLE HANDBOOK 



other tool specially designed to fit into openings or 
to fit projections on top of the head, the valve should 
be rotated through a part of a turn in one direction, 
then through a part of a turn in the opposite direc- 
tion while pressing very lightly on the valve grinding 




Figure 182. — Reaming- Valve Seat. (Courtesy of Harley- 
Davidson Motor Co.) 

tool. A light pressure will avoid pushing the grind- 
ing compound from between the face and the seat 
and will save a great deal of time. This turning back 
and forth should be continued for several minutes, 
after which the valve may be removed and the head 
washed with gasoline. If both the seat and the face 



MOTOR CYCLE REPAIRS 309 

appear a clean, even, silvery grey, the work is finished ; 
but if dark spots or pit marks still show, more of the 
grinding compound should be placed on the valve and 
the operation repeated. Grinding should not be con- 
tinued after the valve seat and face appear clean 
because any further action only results in making the 
faces and seats oval in place of a straight taper. 

Replacing the Valve. — The valve stems, the threads 
of valve caps, and the surfaces of valve cages, should 
be well covered with graphite grease or with a mix- 
ture of graphite and oil before being finally put into 
position. The recess into which the valve cage fits 
should be cleaned of any accumulations of carbon 
or thickened oil. Care should be used to place each 
valve back into its original position, also to avoid 
interchanging exhaust valve springs with inlet valve 
springs. In some engines the same strength of spring 
is used for both valves, yet this may not always be 
so and it will be best to use care in replacement. 

After the work of valve grinding is completed, 
clearance between the bottom of the stem and the 
valve lifter should be measured and readjusted if 
necessary. 

VALVE CLEARANCE 

There is always a slight space allowed between the 
bottom of the valve stem and the top of the lifter 
which operates against the stem. Were there no clear- 
ance at this point, any slight variation in expansion 
of the valve when heated might cause it to remain 
off the seat and to allow escape of the compressed or 
the burning gas. 

Because of the great heat to which the exhaust valve 



310 THE MOTOR CYCLE HANDBOOK 



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Figure 183. — Valve Spring- Mounting's and Valve Adjustments 
(Precision). 



MOTOR CYCLE REPAIRS 311 

is subjected, it undergoes considerable expansion and 
the stem lengthens after the engine becomes hot. 
The exhaust valve and the cylinder itself expand to 
just about the same degree when heated and the 
clearance between the exhaust valve stem and its 
lifter will undergo little if any change between hot 
and cold conditions. On the other hand, the inlet 
valve is in an almost continuous stream of cool 
incoming gas. The cylinder expands when hot so that 
the valve seat in the cylinder is farther away from the 
crankcase and valve operating parts while the engine 
is running than it is when the engine is cold, but as 
the inlet valve, remaining cool, does not expand to 
any great extent, the clearance between the inlet valve 
stem and its lifter will become greater as the engine 
bcomes warmer. 

Clearance adjustments are generally made with a 
cool engine and it will be seen, according to the ex- 
planation just given, that the exhaust valve clearance 
should be set at the amount that is desired for run- 
ning, while the inlet valve clearance should be made 
less than the amount desired for running. It is not 
best to attempt adjustment of either valve with a 
hot engine but this caution applies especially to the 
exhaust valve because a correct setting is difficult to 
secure while the parts are heated. 

The clearance is measured in thousandths of an 
inch. The average setting for the inlet valve is from 
four to six thousandths (.004 to .006). The average 
setting of the exhaust valve clearance is from six to 
ten thousandths of an inch (.006 to .010). If the 
exhaust valve clearance is made too small, the engine 
will have a tendency to gallop, while if the clearance 
is made extremely great, the valve-lifters may be 



312 THE MOTOR CYCLE HANDBOOK 

somewhat noisy. Noise, however, is more generally 
caused by loose and worn parts than by excessive 
clearance for it has been found that a clearance as 
great as twelve to fifteen thousandths of an inch will 
give good results. 

Certain precautions are necessary in adjusting the 
clearance of overhead valves which are operated by 
push rods and rockers. It will be realized that there 
are a number of points in this kind of mechanism at 
which there may be some slack or play and it is 
therefore necessary when measuring the clearance to 
press down on the push rod end of the rocker arm 
so that the total clearance will occur between the 
valve end of the rocker arm and the end of the valve 
stem. In some engines there is a light spring at the 
bottom of the push rod, this spring being designed to 
keep the moving parts in close engagement. Care 
should be used not to confuse the tension of this extra 
spring with tightness of the valve clearance. 

When adjusting the clearance, loosen lock nuts 
slightly so that the adjusting screw can just be 
turned, but leave the nut tight enough to keep a pull 
on the parts. 

i Valve Springs. — Faulty operation of the engine 
may be due to weakened valve springs and in any 
event it is good practice to replace the old springs 
with new ones every two or three thousand miles. 
The valve springs may be tested for strength by 
inserting a screw driver blade between adjacent coils 
while the engine is running. Turning the screw 
driver edgeways will temporarily increase the spring 
tension. If the engine runs better with the additional 
tension it will be necessary to replace the spring or 
to strengthen it. 



MOTOR CYCLE REPAIRS 313 

If the valve spring is found to be more than a 
quarter of an inch shorter than a new spring it should 
be replaced. If the spring has only lost about one- 
eighth of an inch in length it may be strengthened 
with a washer. It should be noted that exhaust 
valve springs are usually heavier than inlet springs, 
especially when an inlet valve is of the overhead 
type. The exhaust spring is made about fifty per cent 
stronger than the inlet. 

Valve Cages. — Overhead valves are carried in a 
cage which supports the valve and its spring. The 
cage is then mounted in the cylinder casting. When 
a caged valve is to be ground the work can be most 
easily done by catching the end of the valve stem 
in a vise and then rotating the cage between the hands 
during the grinding operation. 

It is necessary that the valve cage make a per- 
fectly tight joint with the cylinder casting and this 
usually requires that the cage be ground into place 
whenever it has been removed. This grinding requires 
the use of only a very little compound and the work 
should be continued only ' long enough to clean the 
surfaces and make them a good fit. Sometimes it 
will not be necessary to use any grinding compound. 

After the cages are fitted both the cage and cylinder 
recesses should be thoroughly cleaned of all traces of 
grinding compound. The shoulders which come in 
contact should be covered with a thin coating of 
graphite and oil. When the cage is put in place it 
should be turned around to distribute its graphite and 
oil, then brought into its proper position and fastened. 



INDEX 



A 
Adjustment (see name of part) 

Air lock, oil pump .99 

Attachments, power 261 

B 

Baffle plate, oiling 90 

two-cycle engine 73 

Battery, ignition from 160 

storage 160 

storage, care of 170 

testing 166 

Bearing, hub . . . . , 2^9 

roller, repair of 295 

Belt adjustment 223 

drive 223 

pulley 224 

Berling magneto 144 

Bosch magneto 148 

Bowden control 246 

Brake 26, 227 

adjustment of 232 

engine as a 235 

Breaker 127 

adjustment (see name of make) 

Breeze carburetor Ill 

Briggs & Stratton motor wheel 261 

Brushes, dynamo, care of 178 

C 

Cages, valve 313 

Cam, valve operating 54 

Carbon removal 282 

residue, oil 86 

Carburetor 107 

air valve, type of 110 

Breeze Ill 

314 



INDEX 315 

manual control, type of 118 

plain tube, type of 114 

troubles with 122 

Schebler 112, 118 

Zenith 116 

Chain, adjustment of 220 

alignment of 221 

care of 218 

renewal of 222 

Clearance, valve 309 

Coil, induction 127 

Color, oil 86 

Clutch 18, 192 

adjustment of 199 

free engine 210 

trouble in 199 

use of 197 

Cold test, oil 86 

Commutator, dynamo, action of 174 

dynamo, care of 178 

Compression, loss of 302 

release valve for 64 

stroke 30 

Condenser, ignition 131 

Connecting rod 44 

aligning 288 

Control, flexible wire 246 

Cooling, air 14, 38 

Crankcase, assembling the 299 

cleaning the 101 

pressure, relief of 50 

Cycle, four 30 

two 68 

Cyclemotor power attachment 271 

Cylinder, arrangement and number of 33 

design of 38 

measurement of 279 

removal of 279 

scored 280 

Current, generation of 172 

Cushion sprocket 225 

D 

Displacement, calculation of , 67 

Distributor, ignition 135 

Dixie magneto 150 



316 INDEX 

Drive . . .22, 192 

belt, care of 223 

chain, care of 218 

Drive, worm gear 226 

Dynamo 160 

care of 178 

principle of 172 

regulation of .176 

E 

Engine 12, 28 

four-cycle 30 

four-cylinder 36 

opposed cylinder 36 

two-cycle 68 

two-cylinder 34 

Exhaust stroke 60 

valve timing ... ♦ . # 64 

F 

Fire point, oil 86 

Firing interval 48 

Flash point, oil 85 

Flywheel 44 

alignment of 297 

fitting of 295 

Forks, front 239 

rear 242 

Four-cycle, principle of 30 

Four-cylinder engine 36 

Frame 24 

Free engine clutch . . . . 210 

Fuel system (see also carburetor) 14, 104 

G 

Gasoline 104 

Gear ratio 222 

Gear-set 20, 202 

operation and care 213 

planetarv 212 

Gear shifting 213 

Gears, timing 61 

Gravity specific (see specific gravity) 

Grinding, valve 305 



INDEX 317 

H 

Horsepower, four-cycle 65 

two-cycle 79 

Hub, construction of 248 

Hydrometer, use of 166 

I 

Ignition, battery, type of 160 

magneto, type of 125 

system, parts of 16 

trouble with 156 

Inlet stroke 30, 58 

valve timing 63 

J 
Johnson motor wheel 266 

L 

Lacing spokes 251 

Lifter, valve 52 

Lighting, dynamo 160 

Remy system 180 

Splitdorf system 188 

Lubrication (see also oiling) 14 

M 

Magneto 125 

Berling 144 

Bosch 148 

care (see name of make) 

construction of 132 

Dixie 150 

drive for 143 

Johnson motor wheel 266 

setting and care of 143 

Simms 153 

trouble with 156 

Motor wheel, Briggs & Stratton ?ftt. 

Cyclemotor 271 

Johnson 266 

O 

Oil, characteristics of 83, 84, 87 

pump, adjustment of 97 

air lock in 99 

engine driven 94 

hand operated 100 



318 INDEX 

renewal of 101 

Oiling 83 

force feed 90 

general instructions for . . 237 

methods of 88 

two-cycle engine 76 

P 

Piston 43 

fitting of 285 

head, area of 67 

repair of 283 

rounding 288 

squaring 289 

pin 44 

pin, fitting of 287 

pin, repair of 283 

ring 43 

ring, fitting 292 

ring, repair of 291 

Planetary gear set 212 

Plug, snaik (see spark plug) 

Plunder oil pump 94 

Power attachments 261 

plant, parts of 12 

stroke 32 

stroke, interval between 48 

Pulley, belt 224 

Pump, oil 94 

adjustment of 97 

hand operated 100 

R 

Ratio, gear 222 

Rear suspension 242 

Regulation, dynamo 176 

Release, compression 64 

Remy lighting equipment 180 

Repair (see name of part) 

Roller bearing repair 295 

Running gear 24, 237 

S 

Schebler carburetor 112, 118 

Side car 272 

alignment of 274 



INDEX 319 

attachment of 273 

capacity of 276 

driving 277 

Simms magneto 153 

Sliding gear system 202 

Spark plug 138 

cleaning 141 

gap of im 

trouble with 156 

Specific gravity, battery 166 

oil 85 

Splitdorf lighting equipment 188 

Spokes 250 

lacing 251 

Sprocket, cushion 225 

Starter, kick 22, 215 

Storage battery (see battery, storage) 

Stroke, compression 30 

exhaust 60 

inlet 30, 58 

power 32 

Suspension, rear 242 

T 

Tappet (see valve-lifter) 

Third brush regulation 176 

! Timing by inches or degrees 62 

exhaust valve 61 

gears for , 61 

inlet valve 63 

magneto (see name of make) 

valve 58, 61 

Tire, care of 258 

construction of 253 

inflation of 258 

repair of 259 

removal and replacement 256 

1 Tools, repair 278 

Transmission (see gear-set) 18 

Trouble (see name of part) 

Two-cycle engine 68 

horsepower 79 

oiling 76 

troubles 80 

Two-cylinder engine 34 



320 INDEX 

V 

Valve 51 

arrangement of 55 

cages for 313 

grinding of 305 

clearance for 309 

crankcase relief 50 

lifter 52 

location of , 55 

parts of 52 

refacing and reaming 306 

removal 305 

springs 312 

stem clearance 302 

timing of 58 

V engine 34 

Viscosity, oil 84 

W 

Wheel, alignment of 250 

construction of 248 

Wiring (see name of instrument) 

Worm drive 226 

Wrist pin (see piston pin) 

Z 
Zenith carburetor ............. 116 



306 90 








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